Disgusting Contract

I have joined gym with gym company in 2016 June, it was a three years contract. they told me the first month is free. now my contract was supposed to be ending month end June 2019. I went to them to cancel, they are now telling me the contract is ending month end July, when they told me the first month is free, that's their way of getting customers. I'm not happy at all. I don't want to pay the July month.