I genuinely thought this was about one of my sisters. What I did with my asshat father was send him one final email. I wrote it as though I was emailing an employer - very formal, very calm, no name calling or rudeness, just “for reasons x x and x, I have no reason to continue this relationship and henceforth consider it terminated. Do not contact me again.” Then move on. Don’t respond to any messages. Don’t even read them. Refuse to engage, and they lose.