I'm being "stalked" and "blackmailed"

Ever since I had given my social media info to my "friend", he started to make fun of every thing I post, I like or reply to. For example, I replied to artworks, only to be called a weirdo for the next 2 weeks. When I post something, even when it's asking for genuine help for my other suicidal friend, he screenshots it and spam it in my DM, even going as far as group chats (this post can be one of those too). He also repeats phrases from my posts/replies, like a parrot (This happened to one of my post asking for help for the suicidal friend I mentioned). Taunting me 10 hours a day, 5 days a week. Blocking wouldn't work, as it's non-existent on twitter, and he can also hide his new identity whenever his account gets blocked my me. I can't really leave twitter, since I had a lot of important things on it, and I really can't get used to bsky. I also can't ask for help from anyone, as they never take this seriously (that's why "stalked" and "blackmailed" are in quotes). Nothing can stop him, so all I'm asking is a good mindset and tips on how to live with this bastard.
"I'm not going to stop and will keep doing so for as long as I can. That's the risk of going online"
Sorry if this is poorly organized or worded, but I really can't express it without sounding like a trauma dump