So when I select "None" after setting up my payment information it just tells me it's an "Invalid Payment Method" Please help me...

So I set up my iPhone and Payment information and I bought some stuff. I still have money on my card and when I decided to change my payment method to "None" because my card not working anymore and says I have to put in my security code again and when I put it in and try to save It says: "Invalid Payment Method. Your payment method was declined. Please enter valid payment information." I have checked my payment information at least 100 times and it still says that. So when I select "None" and I press save it tells me: "Invalid Payment Method. Your current card type is not supported by this store. Please correct your credit card information." Please advise me on what to do.