********** contract

I signed up with Planet Fitness at the end of 2015 or 2016 during a Black Friday special. when the contract was explained to me I was never told that it was a 24 month contract and that I would have to pay a cancellation if I decided to cancel. I was also told on the day that I would have to come to the gym before Saturday the following week to activate my membership. I never set foot in the gym and when they debited my account at the end of the month I reversed the debit order. They called me only once to ask why I reversed it and I explained the above and I never heard from then again. Now I receive a call from debt collectors saying I owe Planet fitness about R4000. This is *****, how can I owe them if I was never a member of the gym and the full terms and conditions of the contract were never even explained to me.