Contract expired, now Cell C charge me even more!!

I had a data contract with Cell C that expired on 13 Feb 2015 at R98.99 per month. On 13th Jan 2015 I wrote to Cell C to ask what my options are, and what I must do to cancel the contract. They did not even have the decency to write back to me. In stead, they tried to phone me on my data number! The Data ****le cannot receive calls, and I gave them my cell number in big red letters. Eventually I spoke to someone who was just interested for me to renew. I categorically said no, the service is too bad and the data signal even worse. Now the contract expired on 13th Feb 2015, the service was stopped. I am now suddenly billed for R279.00 for Feb for a service I do no longer have!! I did not use the data in Feb so there can be no charge!! I emailed Cell C again querying the bill. No need to say, they did not respond. My advise to you reading here, STAY AWAY from Cell C!!!! I had endless problems with them, and continue to do so now.