Has anyone ever done that where the Comcast representative calls the bluff and cancels the service?
At which point, you hang up. Oops, dropped the call.
The easier way to couch it is "Hey, my bill is just too big, if you don't have a promotion you can put me on, I'm probably going to have to cancel my service." Or even easier: "Hey, your competition is offering me X, what can you do for me?"
This does require a confrontation with real human beings (or whatever Comcast is employing in their stead these days), so it's not for everyone - and that is exactly what Comcast is counting on. But it's a damn sight easier to go into an Xfinity store and say "Hey, I've been keeping track, and next month my bill is going to go up $60. Obviously that's not going to stand, so what can you do for me?" when I was told very specifically by an employee of an Xfinity store, during a business transaction, to do exactly that.