Your Xfinity phone number was probably owned/used by someone before you, which is why you get calls from people like debt collectors. They aren't looking for you, they are looking for the person that previously had your phone number.
I've had my phone number for 10 years and as best I can tell no one owned it before I did, so I've never had a call from someone like a debt collector. On the other hand I briefly had a prepaid phone with a different number and I only had the number for two days before I started getting calls from debt collectors for the previous person to have the number.