How to remove credit card on file after canceling account

Long time Xfinity customer (26 years),  canceled my account in January. The remaining issue I have is, I want to remove my credit card, but neither I nor Xfinity CS agents seem to be able to do it. (Since I'm no longer a customer, and I paid my final bill, Xfinity should not have it in their system anymore).

l'm praying someone here can actually fix it. I've spoken to at least 5 agents over several weeks. They all PROMISE they will get it done. They said wait 24 hours to see it gone. One even promised within 1 hour. But it's still there!!! 2 days ago I escalated and was promised a callback from a supervisor the next morning. Guess what, no call.

Here's the problem. I had internet/tv/phone and mobile. I canceled mobile first and paid final bill. Canceled the remaining sevices about a week or so later. It took another week before services were actually removed, but whatever.

Now I go to remove the credit card and it says I cannot because it's used by autopay in mobile. I go to mobile to remove it, but it says I have no mobile services, so I can't.

Why is it so hard to do what I'm asking? Why do 5 agents insist they'll fix it, but it never happened? No one ever followed up with me, they just close the case and move on.

Is there ANYONE here who can help me? Please!!! Someone at Xfinity can do it, I know it. But no one seems to care because I'm no longer a customer. Typical.