An effective way of revenge could be to pretend (actually, if they're a cable company pretending may not be necessary) to have a bad experience with them and as

An effective way of revenge could be to pretend (actually, if they're a cable company pretending may not be necessary) to have a bad experience with them and ask about your money back or why you've been overcharged/etc, especially if their colleagues are pitching to another mark within earshot.