False marketing

I joined gym company in March 2015 and they told me that 2months is free and they started debilitating on my account end of April 2015.March this year which is 2018 the 36months contact was supposed to be finished but they are telling me that my last month of the contract was in May 2018,by law this is false marketing strategy to make people join the gym thinking its 2month's free gym is actually a lie.Now they are telling me I owe them 3months gym money.Kindly assist.