Bad service

My first cellphone contract started with Supercall in 1997, then Autopage took over (never had any problems, then Vodacom took over their Clients. A year more or less later, all of a sudden receive a bill for R13000. Enquired about that.. immediately gave me R10000 credit ‘goodwill’. I asked for my account to be investigated... what if the next month the same happens? Because you see since 1997 - never in my history have I ever had such a bill. But no that’s not important to Vodacom. So the next month I got a bill for R16000. Numerous mails send to ask for investigation on my account without response.. but I am handed over!! Yes thát they can do!!!! Any person with commonsense can see the History of an account to make the maths!!