Annoyed customer

I'm so disappointed in vodacom, so I bought a cell phone for my 13 year old sister. And it seems she subscribed to buy data worth R100 every month without my knowledge. To my surprise I received a debit order worth triple what I used to pay in January. In February the amount doubled again. Imagine paying 5 times what you normally pay. I'm totally not happy with their service, and they tell me I have to pay that money in full for the account to clear. This simply shows that someone can just ***** your phone and subscribe for 5k data, no questions asked... No verification whatsoever and you have to account for it. It was the first and last time using this network