Update: The admins have decided not to restore my original hijacked account because they feel there is not enough evidence to do so. Oh well. I gave it a shot.
So sorry about the bad outcome, but what exactly did they say?
I believe you used your original email address to send them a message. That would partly be some useful evidence that you are the original owner of the account, and maybe your IP address logs from the previous years.
I still feel you shouldn't give up that easily,
this guy did not, and he got his account back. Maybe make a case about this in Meta board as well.