Overcharged in December for data not requested

I was overcharged in December for extra data which I did not request, I have a 1 gig contract with Cell C which means that I get 512 mb any-net data and 512 mb nite data.. I received an sms telling me that my data was running out and if I would like to purchase extra data I needed to reply to the sms. I ignore the sms and used my external wifi for the last few days of December. To my surprise I was charged an extra R254-52. When taking out my contract I also requested that a limit be set on my account that it never goes over a certain amount. The amount set was R300 (my total bill was R570.92). I emailed customer service on Mon Feb 1 and again on Fri 5 Feb and eventually got a reply on Sun 7 Feb from Kagiso stating that they have received my email and the query has been forwarded to data validation for assistance with a reference number of ***. Today almost 4 weeks later I have still received no response either by email or a phone call to let me know that this matter has been resolved. When I didn't hear from Cell C, I thought I may just get a credit on my account but have just seen that there is no credit that has been passed.