Not once did I say that I didn't believe contract extension was there; in fact, I agreed by saying that I recalled doing it a long time ago.

The post was more confirmation that (some?) debit cards do work for UK customers to pay for their FFXI subscription.

Tamoa and Saefinn also mentioned that they were UK customers on debit cards who have no trouble with their UK debit cards processing the transaction.

Therefore, we can assume one or multiple of the following;

The account is incorrectly set up
The card isn't a valid debit card type
The bank processing the transaction is lazy