Billing more than R10000 and they say its correct

I received a bill from Vodacom stating that my account is currently standing on R10000. I sent in a query just to find out yesterday that it is correct. I asked for specifications but could not be provided with it and Vodacom said that the data line is a open line so if the data is finished it will still continue. However, they did send me a breakdown as to when all this data was used. Just to find out that all the data was apparently used within 5 hours. Every 2-4 minutes R78.99 was deducted from my account. How is that possible? And then, WHY, IF the data line is "open" WHY will it all of a sudden stop after 5 hours, WHY didn't it continue and WHY is this the first time in almost 18 months that this happened? All this data was "used" in the morning hours, I can not accept this bill. I just really want to know why did it start 10:35, continued every 2-4 minutes and stopped 05:45 in the morning.