Refusal of contract cancelation

I took a contract with Cell C in August 2015 which has expired in 2017. I took top up 30 where I was paying less than the original contract. Cell C recently changed the amount that they are debiting in my account. End of October they took R174 which is 4 times the contract amount. I went to Cell C outlet for cancelation I was given call centre number and they told me that cancelation are done through call center. I called on the 2nd of November after the debit order of R174 went through on the 31st of October. The consultant told me that it will take 48hours to show on their side. I called again today I was told the money is still not allocated the system is still showing as I am owing. The consultant told me that they can't do the cancelation as I am still owing. I felf that I am kept against my will on this contract.