Packet Switched Data

My MTN wi-fi account is normally R309.00. In November 2014 I was wrongly billed for R621.94 and in December 2014 for R906.10. According to the statement I used Packet Switched Data, but I did not use my wi-fi for anything other than I normally due. I tried to obtain info and help from four different MTN shops across Pretoria were one shop referred me to the next to sort out my account. Eventually the shop assistants gave up and said I should phone the MTN number for internet queries. I did this in shortly after receiving the December account, and the phone operator told me the problem will be sorted out within that week. I am still waiting for ANY reply from MTN regarding my account queries. I have lodged more than 3 telephonic queries as well as numerous queries through the MTN Active website. This is totally unacceptable and the shop assistants do not have access so it seems that MTN does not have a system to assist its customers.