Alledged data usage

I received my February bill and was quite shocked to see I have an extra R400 to pay for data usage for January. I called Cell C and they didnt seem very helpful to help me investigate this. I then went into a Cell C store, and the people there didnt seem to interested in my query. I did find it insane that I have to pay for R400 worth of data when my data conveniently NEVER worked in January and they showed me when I had data charges and it was at times I KNEW my cell was off and most of it was in the 2 weeks I was at home working off my own home wifi with mobile data turned off at all times. I was told once my 100mb are up my data switches off, which I thought was what happened as, like I said my data never worked. I even bought a mobile router from Cell C which I used at all times I may have been out during January. I lodged an email query with Cell C and after waiting 3 days for them to acknowledge and 5 days later I am still waiting for any form of response regarding this from them. This is plain *******.