unblocked BLOCK

I've been with mtn for many years, I decided to get a contract for daughter she is 11 i remember saying as I do with all contracts please make sure there is a block on her contract because she's on 11 years old. She's had the contract for a year already with no issues at all, also all family and friends have wifi. This month I received a R3000 bill, I was told there was no block on her phone how do I prove this? And how after a year does this only happen, was it unblocked. I feel sick to my stomach to have to pay this money when I feel its jus not true, especially with having wifi. Plesse help on how I can solve this.