Well as far as I'm aware, you haven't signed anything, so I fail to see how they can uphold this "contract" of theirs. It's dirty tactics and unfortunately most of them will do this and worse to get your custom.
A word of caution however - something I found out in my poverty lecture recently (like I need a lecture in it - I live it!). A lot of the phone calls and doorstep calls are for a simple reason and it's not necessarily to get your custom. They actually make a note of anyone who says that they're unemployed, on a pre-payment meter or in debt to their energy company and you're then put on a list of "undesirables", they're actually out looking for those customers they want to avoid. Another measure is that a lot of the computerised phone systems are programmed so that those customers they don't want to speak to i.e. those struggling to pay etc are left waiting the longest and those wonderful customers they love are answered straight away. Straight from my lecturers mouth, I kid you not. So don't do what I've been doing which is telling them all I owe thousands to my energy company just to get rid of the pushy so and so's, it could come back and bite you on the bum!
