Other people reblogging old art/deleted posts is impossible to control. Actually, if you had kept the posts, you would have been able to turn off reblogs, only on posts that are NOT deleted (this is a setting now on individual posts), but because you deleted them there is nothing you can do. I would recommend you go through every post you've ever made that is still up and remove the ability to reblog them, for your own sake. They will still be visible, but won't be able to permanently circulate anymore.
Also, I would like to say, no one reblogs art posts to get likes. People reblog art to keep an archive of art they like on their blog. They want to show it off, not to say it's theirs, but say "I love this thing and want everyone else to see this thing I love" and your url is still credited under every reblog. Because reblogs are an inherent part of Tumblr, Tumblr is never going to totally delete a post! Even if the original creator deleted it! Tumblr will very very rarely delete a post so that it can't be circulated in any way, and in most cases only does so if the original poster was banned from the site entirely, even then it can still circulate, it is just glitched and doesn't have notes.
In general, you should treat the internet like whatever you post (text, images, etc) will be on it forever, but platforms like Tumblr are especially designed for the longevity of content. I would suggest you consider this every single time you post anything. I don't think it's fair of you to call someone out for using the platform the way it was designed - if they were "reposting" and pretending they drew the art, that would be 100% bad. If they were reposting and removed credit to you, that would be 100% bad. But your credit is there with every reblog, and you do not actually get likes from reblogs. The person is clearly just a fan of your art and wanted to be able to find it easily again.
You may not be a fan of your own art anymore, you may not want it to circulate anymore, but the reason people reblog it is because they find something to like about it even now. You might be sick of reposters, but because you are a talented artist, it is unfortunately inevitable. Even if it wasn't reblogged anywhere - I guarantee your art is on some other website still. Or even google images. You just have to make peace with that and either
1. stop sharing fanart at all or only with a private group of people you trust or
2. only post new art on platforms without a "reblog" system like Twitter or Pixiv, even if it will probably still be reposted somewhere else, at least if you see it on Tumblr later you can get it removed as you can claim copyright infringement. (but only if you didn't post it yourself already to Tumblr, even in the past, since reblogs don't count as "repost")
At least on Tumblr, when someone reblogs, it always links back to your original account even if the post was deleted. That is not the case for google images or Pinterest or the many other sites that exist to host art.
You can try, but you ultimately can't control what people do with your art once it's online. You can't have it both ways where you have 100% control but also get lots of likes and engagement. The more people see your art, the more likely it is they will do things you don't want them to do. You can report copyright infringement, but the Tumblr reblog system itself is not copyright infringement. That's it. And harassing someone by publicly @ ing them for using a website the way it was designed is not okay, even if you feel uncomfortable and hurt. I'm not saying reposting is a good thing, but in the first place, the assumption on Tumblr is that reblogs are always okay if it is possible to reblog a post. Back in the day, you used to have to ask people not to reblog and just hope they would be polite. But now you can literally remove the ability to reblog posts, so in general there isn't an excuse to get mad at people. All you can do is block them, if you don't like what they say in a reblog, or don't want someone to reblog your work. No one sees "reblogs" as "reposting" because it links back to the original posters blog. The image is copied to another blog, yes, but if you hadn't deleted the posts, all of the likes would go back to you. Even then, as I have stated before, no one reblogs for the sake of "getting likes" or whatever you think. "I" get like 1 or 2 likes max per reblog, but they don't go to "me", they go to the post and the original post's owner. Only the likes of original posts are counted as "your" likes. But since you deleted the post, they just go back to the post and no one else. The likes aren't recorded as "so and so's likes" they are recorded as the "notes" on a post, if that makes sense. It's like when on Twitter you can see if someone liked a retweet you made, even if you didn't actually tweet whatever it is yourself. It's just telling you that someone you follow "liked" that you shared something, you don't get to "keep" the likes.
I apologise for the long post, especially since English is not your first language, but I hope you can understand this point of view. I empathize with your position, but you should never have posted to Tumblr in the first place if you wanted to keep 100% control of the spread and distribution of your work. You shouldn't post at all if you aren't prepared for that. It's not just artists - people who write embarrassing text posts, or post selfies when they were a kid, all of that is on here forever. Even porn, which was banned, still exists now if you can find a blog with porn on it, it just doesn't show up on the search. Stuff lasting is part of the identity of Tumblr. As much as you can say in your bio "please don't reblog", it isn't against Tumblr guidelines to reblog deleted posts. And because Tumblr's culture is based off of reblogging, there is a high chance people wouldn't understand what you mean by "don't reblog" if the option to reblog is still there, or not even see it in the first place. I almost never check the bio of an artist I'm reblogging from, anyway - this is very likely to be the case of most people too, unless they really like your art and want to see more. That's the only reason people would look at your bio or your pinned post, because they want to see more. And that's the problem - people want to see more, forever. I'm sure the person will delete their reblogs because you called them out, but can you really do that with every person who reblogs your old art?
I'm very sorry if this comes across as rude, but I hope you read the whole thing and think about it carefully. I don't want the world to be full of people who disregard your autonomy and your wishes, but it is extremely unfair to publicly shame someone, especially someone who isn't an adult, for simply using a site the way it was designed. It's not "the state of the site", it's the way the site has ALWAYS worked. Tumblr does not see reblogging as stealing - and it never will. Especially when it gives them no monetary gain, no fame, nothing. It all goes back to you. And if you hadn't deleted the posts in the first place, you would have more control over them now.
Context for other people seeing this later: the person aukives is calling out in their second reblog did not repost. they simply reblogged 20ish art posts that aukives originally posted but later deleted, which they found through reblogs other people had made before the posts were deleted (or they had a reblog in their drafts before it was deleted). There is no indication the reblogs were made for malicious reasons, but only because the reblogger is a fan of the cartoon series the art is of. Aukives URL is included with every reblog, and you can find the blog immediately like normal that way. It doesn't seem like the reblogger ever makes original posts so they aren't clout chasing or looking for notes, and likely just want to create an archive of their favorite thing like most people who use tumblr do.