Honestly. I've just had a call from someone at mychild.com, whom I registered with a few days ago, trying to offload some educational CDs for free if I subscribe to their mag. I wouldn't mind but I ticked the box that said no to those kind of shinanigans.
if they are a british company registered here then they have broken the law as you ticked the box, if they are abroad though, you have no chance except to 'unsubscribe' (which can take several weeks to be registered strangely enough)
if they have a 'contact us' section, e mail them and complain, I had a quick look on the website but couldn't even find where to join