I recently did this with Charter as AT&T is also in our neighborhood. The person at Charter first tried to do an up-sell (which would have cost more money) and eventually came around to saying that they wouldn't offer the lower rate again. At which point I said, "I'm going to AT&T who will give me a better rate, cancel my service." Which resulted in a slightly rude interaction before they canceled my service. A week later AT&T internet was up and running.

It's was a very odd interaction given that Charter's fine print says that to qualify for the discount you have to not have subscribed to Charter's services for a mere 30 days[0]. Even with limited competition, now with MiFi hotspots a person could cancel their plan, do a pay-as-you-go MiFi hot spot for 30 days, and then resubscribe with the new rate. (Not sure if Comcast is the same.)

[0] "Offers are valid for a limited time only, to qualifying residential customers who have not subscribed to applicable services within the previous 30 days and have no outstanding obligation to Charter."