Unfortunately, the same medium doesn't imply parity ("To cancel, please solve this math puzzle to prove that you are not a robot"
Then it is not as easy to use as the mechanism you used to sign up, and it's now against the law.
Yet, it's the same media.
Sure, "the same media" is already something. I remember a supposedly no-strings attached phone company that you could only cancel with a plain old snail mail (that was in EU by the way, for those of you who believe EU is the paragon of consumer protection).
I wish it were that simple. The language I quoted gives two additional requirements, however, and no examples for what does/doesn't meet them.