Anyway, even if I don't get my account back, I don't want him to use my account and post on my behalf.
Click the link in the email to lock the account.
I have already done that. It is locked but does he able to claim the account just because he provided a BTC signed message signature in this thread. I am not able to provide one as I believe the provided wallet addresses of mine are deposit addresses for crypto exchanges. I have never shared my personal wallet on bitcointalk.