This is way too much effort, unless you happen to enjoy yanking some chains over the phone.
Here's how you quit Comcast:
(1) Disconnect every piece of Comcast equipment in your home.
(2) Load it in a box, and put the box in your car.
(3) Drive to the nearest Comcast customer center.
(4) Dump the box on the counter and tell the rep: "I wish to terminate my service immediately."
No one will argue with you. You have completely bypassed Comcast's customer retention process by doing this. Pay the amount due on your bill, get a receipt with a complete list of the equipment you've turned in, then go home.
The process Comcast has for this involves:
1) Finding a customer center that's open when you're available
2) Returning the equipment to the counter
3) Take a ticket
4) Wait 1+hrs while other people complain about their bills
5) Get confirmation from the customer service rep that your account is in good standing and now closed