ICloud payment for storage.
I keep trying to update my debit card information under my iCloud for extra storage and it won’t allow me to delete the current card on file or allow me to add my new card.
iPhone X, iOS 12
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’)