Sky high bill!

I took out a 1Gig contract for my 12yr old son about a year ago. He's always remained within the contract amount and I've always received the correct billing until now. I was shocked to get a bill of R 15419.34! He uses the wifi at home when he does make use of the ipad and most of the time he uses the desktop or phone. I cannot fathom how this is possible as the iPad is hardly ever in use. Called the call centre and needless to say, I got no answers! How can there be no limit on a kid's contract? The call centre agent says a message was sent to the iPad but he doesn't have an apple id so the message was not delivered to us. He cannot access messages or download anything because there's no Id. Why did Vodacom allow the amount to escalate to such an amount? Surely they could've called to make sure we were aware of the data being used? Why can't we get itemised billing of data used? Where's the proof? Pathetic response from an uncaring agent fostered by a company who cares even less!