Comcast also has deployed this other trick where you call them for support, they'll just say they can't do anything if you use your own modem. It's malicious incompetence.
Oh for business users they'll offer to send someone with the threat that if it's anything on the premises or it is an intermittent issue resolved by the time they get there then they'll tack a $100 charge on.
EDIT: I've written before about an issue caused by a miswritten provisioning file on their end that involved eventually writing their executives to get it resolved: https://news.ycombinator.com/item?id=35595663
EDIT: I've written before about an issue caused by a miswritten provisioning file on their end that involved eventually writing their executives to get it resolved: https://news.ycombinator.com/item?id=35595663