Cannot remove card

'If you can't remove your last payment method or use no payment method with your Apple ID' click here --> https://support.apple.com/HT203905

If you are updating an old card and have ongoing subscriptions you may need to first add the new card and make it the primary payment method before deleting the old card.

If you have an ongoing payment or subscription, then you can not remove your card. Go to:

Settings -> Apple ID (Your Name) -> Subscriptions

Check if you have any ongoing subscriptions.

If you subscribe to iCloud Storage, then it must also be canceled first before you can remove your Credit Card.

More info about removing/changing Credit Cards.

https://support.apple.com/en-us/HT201266