How would the administration know that someone stole the account from you if there is nothing that connects you to a period before the theft happened? They can't just trust you on your word. You need some proof. If you walk into a police station and say your neighbor is a bank robber, the police isn't going to get a SWAT unit, knock his door down and arrest him. They will want to know how you know that and what proof you have.

You can prove the account is yours by signing a message from an address you posted in the forum in an unedited post.