If you find that the number of characters that you can create has unexpectedly increased, then you may have accidentally obtained an additional Content ID. Please be aware that you will be charged a fee until you terminate the additional Content ID. In order to cancel a Content ID, access the SQUARE ENIX Account Management Website (https://secure.square-enix.com), click on the FINAL FANTASY XI tab, select the "Options List" for the PlayOnline ID associated with your characters, and cancel any additional Content IDs on the following screen:

The option you should choose will look something like this: