Here in The Netherlands there's a law that you should be able to cancel the same way you signed up. Signed up through a web form? Should be able to cancel through one. If they don't offer it, the closest alternative is valid. Just send them an e-mail with the relevant information and you've legally canceled. Doesn't matter whether they like it, accept it or respond to it, the subscription is void. If they keep collecting money, just reverse the charges. They'll have to sue to actually get your money, which they'll never do, because their lawyers aren't stupid and know that they'll lose (it has actually happened).

It wouldn't surprise me if this actually originated as an EU regulation instead of national law.