Your account has never been banned. There are two common reasons that might be preventing your login:
The first is that maybe you (or someone else) tried to log in too many times with an incorrect password. This causes a temporary IP lockout. Wait 30 minutes to 1 hour and try to log in again, or if you cannot remember the password, you can reset it at https://en.nostalrius.org/password.
The second is that you may have an IP address that is being declined due to a country IP lock on the account. Country IP locks are a new feature that have been put into place to help prevent account hacks. You can reset your country IP lock using the password change feature as well.
Same thing happened to me. I changed my password last night and switched country lock to USA, wouldn't let me log in this morning. I changed my country to no lock and I can log in.