Problem with updating payment details

I need to update payment details. When im trying to update my card details, they say that your payment method was declined. Please enter another payment method. Then im trying to delete my payment method (bank card) they say: There is an active subscription on this account that requires at least one payment on file. How to solve this problem, becouse there is a lot of data in iphone and it cant be stored in icloud, becouse i cant buy more GB becouse of this