Contract suspended

I joined virgin active at the end of May, with a monthly payment of R500. I couldn't continue with my gym due to health problems. In August i made an debit order request to deduct R1000 for the two months that was outstanding which was July and August, but the debit didn't go through due to insufficient funds. At the end of September I requested to have my membership suspended until I finished paying the outstanding amount and until I am physically fit to attend gym. On the 5th October I called Virgin Active Nelspruit to check the status of my membership, only to find that I am now Owing R5700. My membership is just 4months old, how can I owe such an amount. They said they have charged me for the whole duration of the contract, which is two years. I find it irridicculous. How can one pay for service not rendered?