Xfinity support

I've had an issue with billing and the mobile service from back in 2023. I just got off the phone with Comcast billing mobile billing. They gave me a number to the credit collection agency because they said I need to dispute it there as well and the number that they had given me was [Edited: Phone Number Removed]. When I called that number they said that they do not take phone calls. Did they do not accept phone calls from outside lines which I thought was weird. But my problem is I need to know the credit company that you sold my bill  253.34 . Like I said this is from 2023 and I never had a bill. The whole thing was a big error on xfinity's part. I already handled the part with the billing company which they are taking it off my account within the next 3 days. But they also told me to call the credit company and dispute the bill with them as well. But I don't know what the credit company's called and the phone number is not accepting calls from anybody. So if you could please get me a phone number or the name of the credit agency that you sold the bill to I would greatly appreciate it. Thank you