Refusal to investigate

My cell phone bill for the month of May came and I nearly had a stroke - R2200.00 instead of the normal R400 - R600. R1380 of that for data charges on one day. I manage my data by buying prepaid bundles. I reported this to the brackenfell store where I usually get very good service. her area manager rep**** with a letter that the sim charges is the customers responsibility and data charges increased. I then went to the cape gate branch, hoping somebody can just look into it, so that I can see where the charges came from. Apparently it cannot be investigated - BUT you can try customers service - only thing - they are on strike. OOPS. The guy in store actually had the nerve to tell me I probably downloaded movie clips. As if I wouldn't know if I did? There is NO emotion in the way they deal with customers. This is not my first ordeal with MTN. Customer service is something that doesn't exist anymore