Ridiculous data charges

I queried my sneaky data charges of R756 on 5 January this year for my December 2015 bill. Firstly I received my upgrade of the Samsung J1 on 24 December 2015 and I have always used data through Wifi and have always made sure that the mobile data was switched off therefore I find it strange that my data charges would have accumulated to this amount. <br> <br> I have signed a letter giving Altech Autopage permission to do a full investigation into my account. But to date have not received a response from them. Their call centre is useless and nobody knows what is going on. <br>