1) There is something called slander.
2) If someone is on anon while sending messages you can't confirm who it is (they might be able to)
3) You want this male user to pay, but you could settle for someone else paying for it instead.
4) if it happened 3, 4, 5, 10 years ago or whatever it's pretty meaningless now. Not sure about statue of limitations though or how that would work, when it comes to law.

They do listen. I had to go through Twitter to communicate directly when I was being harassed. Thankfully the user was banned. I don't know if it's the same person creating new accounts to be abusive but if you feel threatened go on Twitter. They'll help you fix this situation. I'm sorry you too have had to deal with toxicity on this platform.

May I ask who? I feel this kind of, I don't know, guilt(?) because I miss things happening all the time and it makes me feel like I'm not supportive or attentive enough, anyway it's terrible to hear and you deserve so much better