Weird... Maybe you signed up with the wrong username and when you signed in, you thought it was something else?

Try a password recovery. Maybe they'll send your username details too. See if they have a username recovery. Ya don't see that much though.

Worst case scenario, change IP and sign up again, or just sign up again. With the amount of people joining, I doubt they're going to go through everyone. Lol. Seeing how one account is inactive, I doubt they'll ban you for making another. If ya wanna be safe about it, just PM a mod on your new account and give them the details so they can deactivate the other account, though it was get disabled for inactivity anyways.