R8000 FOR DATA subscription

Vodacom experience was very very bad. I will never ever take a contract with them. i bought my niece and daughter phones from Vodacom with contract and all of a sudden, they told me that my niece subscribes to data and i owing them R80000 and they went to an extend of making double debit in my account while my account was prepaid. How possible is it that someone can subscribe to R8000 Data. i will never heal from this as for Vodacom you will meat your match one day. I had dispute with them and it was never resolved until i started to pay them what they said i owe them.