I think it's obnoxious that you can't send a cancellation request through your credit card company's website.

Just find the charge, click the "I want to cancel the service that caused this charge". The merchant has to either cancel or reply with a message clearly explaining why they can't do that (i.e. you agreed to a 12-month minimum).

Whoever is collecting the money has all the information needed to make the cancellation request. No website logins, passwords, self-addressed stamped envelope, etc.

Apple has done this for subscriptions that collect money through the iTunes store. It's awesome.

AmEx should do this because unlike all the other cards they control the whole stack.