You should've received an email to the old email address when the scammer changed it. There'll be a link in that email which will allow you to lock the account within 14 days of the change. It won't help gain access but at least it should keep the scammers out.
Here's what I received (with link redacted):-
Dear eXOBeX,
Your Bitcoin Forum (b*****.org) email address was just changed from bitcointalk@*****.com to
sergun1646@yandex.ru by IP address 5.227.166.23. If you did not do this, then you can visit the following link within 14 days in order to lock the account:
https://bitcointalk.org/index.php?action=seclock;u=*****;t=*****;o=*****%3D%3D;n=*****%3D;c=s*****%3D
Note that you will NOT be asked for your password at that URL.
Regards,
The Bitcoin Forum Team