There's only one easy way to cancel service with a company like Comcast. You have to lie and tell them you're moving to a city that they don't serve. They don't transfer you to customer retention and you'll be off the phone in a few minutes.
Anyhow: I was actually moving, told Comcast so, and I was indeed off the phone in a few minutes. "I wonder what everyone's concern about Comcast is anyway," I wondered. Then, a few days later, the "follow-up" calls began. It got to the point that I had to block the Comcast number just to get some peace.