blacklisted me

A debt collecter called me saying I owe the above mentioned company R3500 .The sales person never explained everything thoroughly to me .She practical forced me to sign a contract I did not understand because she was desparate to meet her sakes targets . I didnt understand that I would have to pay regardless of I use the service or not , now I owe Zone Fitness R3 500 for a service I did not receive.Zone fitness never contacted me about this instead they handed my account straight to debt collectors .I was supposed 2 pay 165 per month and I only missed 6 months but I already R3500. How is that even possible ?These people are reaping me off .What they doing isn't fair .The company is exploiting me .I shouldn't be forced to pay for a service I did not receive. I'm depressed because I'm not working .now where am I gonna get R3500 to pay for a service I did not even receive?.