It pretty obviously implies that Comcast thinks that you returned a rented Wireless Gateway box.
Do you (or did you at any time) use a rented Wireless Gateway box from Comcast? Perhaps even years ago (Comcast is not known for promptness when acknowledging the return of rented equipment)?
If you go to »
customer.comcast.com/ and login, do you see a Wireless Gateway assigned to your account at »
customer.comcast.com/MyS ··· Internet ?