Unauthorised continuing of contract

I signed up for a 1yr contract in june 2014. My contract ended 4 months ago, yet planet fitness keeps on debiting money from my account. Nowhere in my contract did it state that they will continue with my contract after it ended, they claim to have sent me an sms but i have not recieved it yet. And nowhere did i give them verbal or written permission to continue with my contract. In short, they stole 4 months payments from me, and they better pay it back.