Help to resolve my billing concern

Sept 8, 2024 - I decided I no longer wanted Xfinity services so I asked the rep for the amount of my outstanding balances so I could pay everything owed to Xfinity and paid (see billing on 9/8/24).  I had a zero balance.  I turned in the boxes on 9/13/24.  I was warned I may get another statement because of when new statements go out and was told it would be credited because my account was paid in full.

After calling around for another internet provider and finding out I would be forced to keep Xfinity if I wanted high-speed internet, I called back and spoke with another Xfinity rep and they offered me another internet package, which was better than what I had previously.  It was setup to begin 9/14/2024 and it was a totally new rate.  Keep in mind my Xfinity balance is 0.00 at this time so my next bill should only be for the NEW Internet package.  

I am being charged a past due amount under my old bill.  Please review my account and correct it.  I have been fighting this battle since Sept 2024, went into a local store for help in December 2024 and now it is the end of January and no one has contacted me, but you keep disconnecting my service saying it is past due.  This is very tiring.  Please respond and advise.  I am asking for Customer Service.  I am a customer.  Thank you.