I need help!

Okay I have a question, I was selling an account and I went first, I gave him enough information to recover the account. He screwed me over and everytime I recover the account he just recovers it back. I've given up on the account and now he has control of it. I created the account with this IP address. If I wanted him to not be able to recover the account what would I have to do?
I would love you so much if you could tell me this.

Sincerely, Adam