Payment information please
Why it keeps asking for information on an older card and won’t allow me to add a new one
iPhone XS Max, iOS 12
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Try adding the new card and removing the old one via https://appleid.apple.com/account/manage
If that also doesn't work contact iTunes Support and see if they can help you do it : http://www.apple.com/support/itunes/ww (click on your country's flag, the country where you live, and which is therefore the country on the account ; click on Contact Support towards the top right ; click on Get Help under 'Talk To Us’)