OVERCHARGED DATA FRO R5000

I suddenly got a bill from Vodacom of R5000. When I phoned they said it was for the data that was depleted. Where is the sms telling me what the data has been DEPLETED? NO WARNING THAT IT HAS BEEN DEPLETED and that we were using extra data now!! No warning of the costs or what the costs is going to be when we use more data. We were not aware of the costs at all. I phoned Vodacom enquiring about it and they haven't given me an explanation at all. Vodacom I need answers, This is unacceptable I have spoken to other clients as well and it happened to them as well. THIS IS UNACCEPTABLE form VODACOM!!! No answers on my enquiry at all. I launched an enquiry two weeks ago already!!!!