Breech of contract billing for cancelled contract

I was contacted by an agent when my cell c contract came to an end in 2017.The lady offered me a month to month contract which consisted of 10G day time and 10G night time at R199 a month. When I cancelled the contract the guy comes up with a story of the contract being 2 years and I need to pay extra an extra to cancel early. When was it told to me that the contract is now 2 years instead of month to month? I will not pay Cell C any more money I had to pay R131.50 to cancel and yet it was never cancelled. Now I am getting SMS's telling me to pay R131.50 to nudebt ref:ND ********** 9.No one knows this Ref. I was told that some one would phone me to resolve this matter.I am still waiting for that call.I want this contract cancelled and stop sending me SMS's. I am not interested in taking anything else from CELL C as they care nothing about the client and just want to make money.