massive bill without explanation

I got a Samsung S5 for about one year now. My phone bill is about R1000.00 every month as a business man. 2monthh ago i received an account ot R4500.00. Their answer was that i am responsible for all down loads. All they could tell me is that i received down loads from Internet, and send me my itemised billing. No information was received from the Internet. The end result was i paid the money.<br> <br> <br> As we nowadays have to keep your children a bay with the latest technology, A year ago I took out a Samsung tablet contract for my 8year old daughter and bought 2 gig data. The amount due every month is R318.00. This month, end may i received a account of R7500.00. <br> Their answer was, you are responsible.<br> As the previous time, i have receive no downloaded information from the internet and have no proof to justify that,. Is this reasonable? Should the sales person selling the phone and contract to me and my daughter who was with at the time, not informed me that we must watch out for \whatever"Is this our service provider in cahoots with Samsung or what? I am afraid to use my sim card"