See: http://www.ofcom.org.uk/complain/mobile/

Thank you for that have been on the phone to trading standards and they say they can get me out of the contract purely because it was miss sold and I have three witnesses to the fact that they told me I could change my tariff at any time to a minimum of £10 a month, 3 are saying i can only reduce it to £30, so lucky for me phones4u lied