Insane invoices and complete lack of interest

Why Vodacom, why? Why are they going to these extraordinary lengths to make my life a misery? Last year we obtained a very expensive contract, Red Premium, from Vodacom with unlimited calls to any network and 10 Gb data. Problem is, Vodacom just cannot figure out how much to charge us for this service. Bear in mind that this is a fixed contract. It can only be so much and no more. Still, Vodacom's invoice would vary by as much as R4,000 from month to month! Umpteen phone calls and store visits have brought no satisfaction. This week they said we should pay nothing until they've sorted out the tangled mess... and then they disconnected us! Added to that, we have moved from the farm to TOWN and the internet service is so poor, we could never use our almost 90 Gb data we pay for from Vodacom. Of course we contacted them and of course they logged a call and of course promised me that I would be contacted by their technicians before the end of the week, which of course did not happen. Please, please, PLEASE Vodacom. just try and supply some kind of service.