To manage your Apple subscription you must use your Apple ID. All functionalities like cancelling the subscription or changing payment methods are disabled for customers with active Apple subscription.
The following links contain some information on how to proceed:
Cancel: https://support.apple.com/kb/HT202039
Purchase History: https://support.apple.com/en-us/HT204088
Add Payment Methods: https://support.apple.com/en-us/HT201266
Please note Customer Happiness Team is not able to support with these requests.