DATA CHARGES OF R8000

I was on the Vodacom App and discovered that between the 30 June and 6th July my child had racked up an R8000 bill in Data Charges. I have contacted Vodacom to query where this data has been used, to which they cannot tell me and also of which towers and also they can't tell me. I took the contract out in December because she required the tablet for school, where she uses the school wifi, at home she uses the wifi and is only occasionally allowed to use the data, which I requested when I took the contract be capped at the 1GB that is included in the contract. I have been under the impression this has been the case, now I get this bill - shocking. In my first call today, I raised this matter and was told I can't cap my contract it is an open ended contract -what nonsense is that? Then my second call was trying to ascertain where and what this data has been used on and again I was told that they can't tell me. A call has now been logged, but this service is completely unacceptable. It has taken me 2 hours worth of calls to still have no answer. A complete and utter waste of my time. Shocking service! The one consultant was even telling me i would need to pay to get an answer