charged after account closed

Just spent the last hour and a half on the phone with billing for a business account.  I settled up the bill on a phone call with Xfinity on August 16th, 2024 as I had closed the account, on this phone call after I paid, I was told all I had to do was turn in my equipment, which I did that week. The business account has now been sent to collections for a missed payment that they charged after my account closed. My ticket number is [Edit: Personal Information] and was working with Maya.  After and hour and a half she refused to let me talk to anyone else and said she was discussing internally but the amount was still owed. She did not get across that I was told on August 16th that I didn't have to pay anything else, but kept telling me there was nothing to be done and the amount is owed.  Again she REFUSED to let me speak to someone else and said her "supervisor Fe" would contact me once she was free, even though shes supposedly been talking with them the whole time. It is incredibly disheartening as our business has used Xfinity for over 10 years that I have been refused help and continue to be lied to.