Bednobs is right, most distance selling has a cooling off period, but if he has recieved his first bill he may have exceeded that time limit. This is a very tricky one. He is over 18, and I presume that he is not in care or a vunerable adult, so he is therefore responsible for anything he has agreed to. In law a verbal contract is as binding as a written one, but only if there is an independant witness (think of the police and why they always arrest people in pairs!) so if someone else heard the offer, it would be binding. At the moment it is his word against the company. My first instinct is to question why the initial contract and terms and conditions weren't sent to him. Go visit your local citizens advice bureau, who will give you the name and number for your local trading standards office, who will help and advise what the best course of action is. Don't be surprised if they already know all about this situation, as these companies usually target an area saturate it and then move to another.
A cautionary tale for all of us. I wish your friend good luck and hope this is sorted to his satisfaction.