Debt Collection

I would like some assistance with a bill that was sent to collections. It was added to my credit and when I reached out to the collection agency they stated they not longer had the account and it was returned to Comcast. Well I contacted Comcast and the agent I spoke to seemed confused and couldn’t help. He gave me a number to call which was a whole other collection agency which did not have the debt. I would like to pay the debt and have it removed from my credit. How do I contact your collections department?