I cant add or update a payment method

If your payment method is declined in the App Store or iTunes Store

If your payment method is declined in the App Store or iTunes Store - Apple Support

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Get more help

• If you disputed a charge from the App Store or iTunes Store, contact your financial institution again to authorize that charge and future purchases from the App Store or iTunes Store.
• If you're outside of the United States, you might need to contact your financial institution to allow international purchases.
• In some countries and regions, your payment method might be declined because of changes to local law. Learn about billing and purchases in Europe or what to do if your card is declined in India.
• If you still need help, contact Apple Support.

If you already tried (to no avail) the steps provided in this support article:--> Change, add or remove Apple ID payment methods, 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 link I posted, where you can contact them using "chat" or "phone" options).

Regards

Giulio