According to the new owner, he won't be paying the amount owed by the previous owner. So the old balance is as good as gone now.

By the sound of it, you're trying to use your old account to log into the relaunched site? I'm not sure if that'd work but my account was created after relaunch and it works fine.

In any case, you should try contacting support as advised by interbtc to get definitive answers.