I shouldn't have to cancel something I never asked for in the first place.
But the real reason I haven't text'd them yet is because I don't trust them
to stop even if I do. Y'know, like some spammers treat "remove me" requests
simply as verification that your email address is valid, and then send you
more junk.

FYI, semi off-topic for this thread, but: SMS spam is a violation of US
federal law. A recent federal court decision held that the same law that
makes junk faxes and some types of telemarketing illegal also makes
unsolicited text messages illegal.