Make sure you have entered all details correctly, including the correct date with 4 digit year.
One person reported that they had incomplete information in their country settings and completing this cleared up the issue. - How to fix payment method - Apple Community
If you still have questions or problems:
Contact Apple. Click here --> Choose your country or region - Official Apple Support 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."
Click here --> Contact Apple for support and service - Apple Support