Your best bet it to contact iTunes support. I have not seen any threads that have a solution for this issue on this website. To contact iTunes support, click on the link below:
The option is there:-
iTunes MAC/PC, go to the store and pull up your account information. From there look at the row saying Payment Information and click "Edit>"
Then the Edit Payment Information window pops up and the top bar should identify card types and on the right a square 'None' button. Click this and then Done at the bottom of the page.
It is similar on iPhone/iPad/iPod.