BLATANT ******ION

I have been trying to sort out a gross overcharging on my account with mtn . i have been to the branch several times , emailed and called . I keep getting fobbed off and told they are legitimate data charges. There is NO way these charges are valid or correct. This is a business account and the debit orders keep getting pushed through without any regard for the queries.We were not informed when the upgrade was done that there would be no cap, yet I have always managed my phone responsibly and kept the bills low. It is a company phone and it can not be abused. My bill has always been between R200 and R300. suddenly in May 2015 it jumped to R1381 without any unusually high data usage or changes in amount of calls .Then June was a heart stopping , 'gonna- get- fired-amount' of R6746.11!!!! I subsequently went into the branch again and ensured that the phone be blocked for additional data use. BUT still July's invoice amount was R1884.34!! My company cannot continue to be ****** like this .I need this investigated and the company account credited for the gross overcharging. I AM NOT PREPARED TO ACCEPT THE POSITION THAT IT WAS MY DATA USAGE. THIS IS ABSOLUTE BLATANT ******ION!