Mislead, ******* to sining a contract

On the 11.03.15 members of the Body Lab Gym in Southway Mall were doing a promotion of a 3 Week FREE Trial at the gym. When I asked them about the contract they specifically said it a free trial and I can only decide on taking a contract after. After reading the document presented to me, I asked them why make me sign something that state it a contract while they are saying it is a free trial.They explained to me that in order for them to give me the free trial I must sign this document. They asked for my account details, at the time I only had my child account details and they said it is ok to give them those for I can always change them later. I further explained that I will not be in town for the next 2 weeks going on holiday I can only redeem the voucher thereafter. I was only aware of the contract binding story after they billed me for the 1st month which I reversed. I then approached them and laid a complaint. When they got back to me they were suiting me for cancelation fee which I have a problem paying. I feel I was very specific that I did not want to sign a contract but they conviced me that it was just a temporary measure that will be change when they get to the office