spring fitness National fitness illegaly changed contract. spring, Texas

2 years ago I went ito spring fitness to try it out. They said I had to pay 35 a month plus start up fee which I did. Then they had me sighn a contract that said it wad 35 a month. 2 days later I told them I didnt care for it. They said I cant cancel because I sighned a 3 yr contract. I pulled my contract out and said no I didnt no where on there does it say 3 yrs. Yhey said there copy does. I told them I have the carbon copy and you cant change that. They added what ever they wanted to it after I sighned and said thats illegal. For 2 years I have tried to get them to cooperate now they have 1300 added up on my credit report. When in went for 2 days. Scam artest alert dont sighn. Next step for me is to try sueing scince I still have the original contract.