If you are using a Comcast supplied gateway device there is no way to change / spoof the MAC address. They do not have that feature.
You likely recently received a new / different WAN (public) IP address assignment to your connection from their DHCP server / IP address pool, and the rDNS / geolocation data that is associated with it is now incorrect for you as it previously belonged to someone else that lived in that area. Comcast shuffles blocks of IP addresses around the country all the time. ISP's don't correct this. A third party service does. Unfortunately this is typically a *back-burner* thing to get corrected. The only thing that you can do is to report it. You can try this;