Cancellation

I joined gym company somewhere in August 2015 after being convinced by their sales representatives to join at Maponya mall. I only went to the gym approximately 10 times but i was still paying their monthly fee of R199 until earlier this year/ . I called them several times asking to cancel but they told me I cant cancel over the phone while I cannot make it to their gym before 6pm to cancel. Now i just received an sms saying I am in a process of being blacklisted. I have paid them over 24 months installments since then while I wasn't even using their facility at all. the last time I went to the gym was before December 2015. My question is what did I take from them to be paying them for something I don't use. i stopped paying this year and they should check they records and stop sending me sms's not to forget to pay. They can check the last time my access card was used to enter their premises. Please cancel that contract and stop sending me sms's. They don't perform the vetting process to determine the affordability. Please cancel my contract. Most of their revenue is generated from people who don't even go to the gym but struggle to cancel their contracts.