Check your subscription in the Mogstation as it will list all the characters available on that account, and if they are active or suspended.

Connected to that, did you change to an 'entry' subscription rather than a standard one, as entry subs only allow one character on a server, and any extra characters after the first that you have if you switch to this cheaper sub are then suspended. In this situation all you can do is change back to the standard one and then reactivate the suspended characters.