Vendors who allow online or over the phone sign ups, but only in person cancellation don't tend to be relying on the quality of their product or service to keep customers.

ISPs are one where if you are not a savvy consumer you wont realize that when they say up to X megabits a second that its not only a different unit from megabytes, but that anything 0 <= (actual service) <= X is considered meeting the terms of the contract. ISPs are also the type of company where you call to cancel the service, as the contract allows because you are not locked in, and instead of letting you cancel they give you the run around and send you to person after person to try to keep you online.

While we don't know if OP was in the right here from this story, you must have at least _some_ ability to see where they could be at fault

I agree, them allowing me to chargeback would have been nice but I certainly understand why they would say otherwise. I was hoping to charge back and then meet the merchant in court when they sued, so I could also collect attorney fees in this case. It was egregious. But, I also understood that Amex may take your point of view. I didn't have a problem with this.

Them stating I can't stop future payments though has nothing to do with any third party contract that may or may not exist. It's not up to them to enforce that, and in any case I can assure you said contract did not list American Express as a payment method anywhere on it. They enabled a merchant to extort me because I had at one time years before made the mistake of giving them my Amex account number and the merchant purposefully made it impossible to remove.