Vodacom over charging us and ignores our complains

I have a contract under Khum Investments and i took the RED VIP Package which gives me unlimited calls and sms and 20 gigs of data for R2 118 PM. over the past year i have gotten ridiculous charges over this subscription. first is when the bill was around R13000-R26000 and they claimed it was open line and i used alot of data, this was not true because i did computer science and im not a clueless about how i use and check my data usage. Now this month i have gigs left but vodacom is charging me R3500 already on my number...how is this possible? this is happening to multiple numbers under the company and we thinking of cancelling the whole thing because vodacom is running around in circles for months with our complains while continuing to over charge us like clock work every month.