Here's what you should do:

1. Move (lower-left) this topic to Other - Meta.
2. If there is one: find an old post with a Bitcoin address, you're going to need to sign a message to prove ownership.
3. Follow the instructions in Recovering hacked/lost accounts

The account got banned in a wave of plagiarism-bans. If the plagiarism was yours, you won't be unbanned. If it was the account thief who did it, you stand a chance.
Until now, I haven't seen any evidence of the account being hacked, but the change of language and drop in post quality make it plausible.