This is exactly why I cancelled my Comcast service a few years ago and switched to Sonic, even though it had orders of magnitude less bandwidth. I even offered to stay on as a customer, and pay whatever 'overage' fees they charged, if they implemented some way to make exceptions and never inject the data cap warning on my account, but they claimed that was impossible. When I returned the rental equipment, I made it absolutely clear that I considered this practice immoral and reprehensible.
If anyone else considers cancelling their service, but has trouble getting Comcast to let them actually do it, just remove your payment method from the account, and let them know that if they attempt charging to it again, you'll sue them for fraud; that'll get your account closed real quick!
The suburb (outside of Seattle city limits) that I live in is a suburban area, density is easily high enough.
My choices are Comcast (up to 1gbit down / 30 mbit up IIRC) or rotting exposed copper POTS (from Clink?) that has VDSL at something around 10mbit down / 1 mbit up.
Thus, I have only one choice of broadband provider and due to lack of competition as well as lack of regulation, no broadband providers that offer unlimited service* (technically Comcast will happily charge me 600 extra dollars a year for no increased speed but no caps; however they shouldn't even bother with caps on their highest tier packages).
I used Sonic (DSL) for five years while I lived in the south bay and I was extremely happy with the service and the company.
Where I live now comcast is the only broadband available and although the service is theoretically faster and somewhat less expensive, I'd pay twice the price for sonic. Comcast is unreliable, intermittently very slow, and the company is impossible to deal with.
If anyone else considers cancelling their service, but has trouble getting Comcast to let them actually do it, just remove your payment method from the account, and let them know that if they attempt charging to it again, you'll sue them for fraud; that'll get your account closed real quick!