Zone fitness

My 17 year old son was cheated into signing a 2 year contract , the salesman used a adult to "stand" for my son , my son was told he can cancel at any time due to his age. They even made him sign to give them permission to debit from his account... Now they refuse to terminate the "contract". I've asked them numerous times and explained to them it's ******* wht they doing but they are head strong scoundrels. PLS help