This document explains how to 'Change, add, [review,] or remove Apple ID payment methods' on an Apple mobile device, a Mac, or a PC; click here --> https://support.apple.com/HT201266
'If you can't remove your last payment method or use no payment method with your Apple ID' click here --> https://support.apple.com/HT203905
If you still have problems Click here --> https://support.apple.com/choose-country-region/media-services Select your country, then a product. If you don't see one that handles your issue then keep experimenting with selections until you reach one that gets you a chat session or a telephone call and get the representative to redirect you.
or:
Contact Apple for support and service --> "See a list of Apple phone numbers around the world." - https://support.apple.com/HT201232
Additional resources:
'Payment methods that you can use with your Apple ID' --> https://support.apple.com/HT202631
'If your payment method is declined in the App Store or iTunes Store' click here --> https://support.apple.com/HT203005