Overcharge - Data

My bill for the month is 2000% more than usual. It is not possible for Vaodacom to let me know whare the data was used and therefore i can not trust the account. When i asked them when the majority of the data was used, they said that it was on a Saturday of which we did not even switch the computer on. Vodacom says that it is virtually impossible to tell me where that data was used on, and therefore it is vitually impossible for me to prove that i did not use the data. I will cancel all my account with them.