R8000 data charges in 1 month without notification

I've been a loyal customer of Autopage for over 15 years. My contract bundle account never went over R700-750 per month. I go in to upgrade after receiving sms and to my surprise was told there is an R8000 additional charges for data. I had not received any warning or notification that my normal usage is being exceeded. I tried everything but I was too late the debt order went off and I lost R8000,00 just like that. I lodged numerous complaints and account queries where registered (I have the call reference numbers) and nothing happened. The store could not help (change from contract to top-up), the many calls have done nothing and the bill just keeps coming in excess of what I normally pay. I have now switched off all my mobile data usage items on cell and computers and am curious to see what happens. In the mean time I have to wait till my contract runs out before I move to another service provider. It is just unacceptable that there is no warning service when normal data is exceeded. I still get the Upgrade sms though!