Remove credit card numbers from the account!
I tried changing my credit card number and it said it was invalid! My other credit is not not valid!
iPhone 11
As per this support article:--> If you need to change or update your Apple ID payment method you need to add the new credit card then delete the old one.
If the issue persists, I suggest that you contact iTunes Store Support Team directly, using this specific link:--> Apple Support
(if you get no help, look at the bottom of the above link, where you can contact them using "chat" or "phone" options).
Regards
Giulio