Is MTN *****ing my money?

I have been billed for approx. R5 000 two months running. Yet my average spend over many years is about R1 500 p.m. I am part of a large corporate account of a top 40 listed company, but in spite of numerous requests MTN has not responded with a detailed breakdown of how this is possible. If they do not or cannot offer an explanation, surely one cannot but wonder whether they *****ing one's money, in plain sight?