Adding or updating payment method issue

I have been having difficulty in either adding new method payment or deleting the presents method payment as it’s pop up “ there’s an active subscription on this account that requires at least one payment on file” . I can’t change to another debit card and also can’t delete the active debit card payment to add another new debit card payment method. My iCloud storage account is full. It very frustrating can’t can’t backup again on my iCloud account. Please kindly assist.