Assuming you have Comcast equipment if a local service center is accessible it might be worth your time to walk in and drop the equipment off when you cancel. There can be a long tail on these if you have to send back equipment. The folks working the counter at these places also don't have a "retention specialist" they kick you to.

I have to say I canceled Comcast for a few months between houses my experience was pretty painless, I called in and they in-fact even sent pre-paid shipping boxes to return my modem and cable box.

Heck considering the profile this call is getting I'm guessing their "retention specialists" are going to be pretty light touch for a while.