Sent to collections over a closed account and equipment I never took delivery of

I cancelled my account in August of 2024.  Xfinity continued to bill me.  I called a minimum of five times to get it taken care of and was assured I would be getting credit back.  That never happened.  In addition, they claimed I had their equipment and kept threatening me with paying them.  I have never used any Internet providers equipment and have ALWAYS purchased my own.  This was explained to the agent and they were not able to provide proof that delivery was taken of their equipment and the records indicated that there was proof that it was not used, therefore confirming that I had never taken delivery of their equipment.  I am now being sent to collections.  I need an agent to properly take care of this or provide me a detailed billing of what, in their opinion, is owed.

Thank you in advance for your assistance.