Xfinity mobile credit card charges after my account closure and can't turn off autopay

It has been four months after I closed my Xfinity mobile account, but the Xfinity mobile website doesn't allow me to turn off the autopayment option or delete my credit card information there. And, I keep receving the bills after the account closure, and the fee was charged to the credit card every month after the account closure.

Each time, I had a chat with an agent, and they refunded the fee telling me that it won't happen again, but the same situation happens again and again. Today is my fourth time to have a chat with an agent because of a new credit card charge from my closed Xfinity mobile account. I am really stressed with these charges every month, and I can't repeat this forever. Please STOP this monthly charge for a CLOSED account.