Hi -- From 1st October 2008 the new revised "doorstep selling regulations" were introduced and apply irrespective of whether the visit to your home was solicited or unsolicited. I would challenge the validity of the contract you signed on the grounds above and that your contract does not state clear written notice of your 7 day right to cancel....therefore it is a unenforceable contract, as listed below by taking the contract along with the new regulations to your local CAB.
http://whatconsumer.co.uk/doorstep-selling/
The Seller’s Obligations
With any contract or sale made in this way, you must be sure you have been presented with clear written notice of your 7 day right to cancel, at or before the time the contract is made. If you have not, the contract is legally unenforceable, even if a deposit has been paid. This notice, which cannot be in the form of small print, or otherwise disguised, must also provide a cancellation form and advise you on how and to whom a notice of cancellation is to be made. Any related credit agreements will also be cancelled. .