internet selling advertising 7 day rule?

I was recently contacted by an advertiser offering an line service, a rep called and basically I signed up after two hours of selling, I was sent an email to confirm that I understood what I was buying and I sent an e-mail back confirming the order. This was on the 5th Nov, on the 11th I sent an e-mail saying that I didn't want the advert after all, I also put this in writing and by telephone call. I was informed that it would take 30 days to get my money back, £350.00, I cancelled the standing orders that were set up and waited for my money back. Tonight at 7.10pm a rep rang and asked why I didn't want it anymore, I told him I'd changed my mind after finding adverse reports on the internet regarding their company, he then said that i had taken too long to cancel, which I denied and he also said that they would take 20%, and that I was aware of this fact, which I'm not. I've told him to ring again tomorrow in office hours and that I cannot answer his questions about whom I spoke to at head office at 7 o'clock at night. I need help please with this, I cannot afford to loose this money, business is tight as it is. Many thanks in anticipation of good advice.

Many thanks for your prompt reply. This firm is Touch Local, we were the 1st customer of this new rep, he wasn't sure what was what and neither were we unfortunately. He was in a hurry to get to his next client which was at least 20 mins away and it was all a bit rushed, (repent at leisure comes to mind)! There contract is very one sided on reading it all now, 20% of the full fee of £870. 00 is due on cancellation, I can ill afford to throw this money away. I did a search on touch local after the rep had gone and got very bad vibes from dissatisfied customers, don't know what to say to this geek when he rings today, he was very forceful.