Extreme out of bundle charges

It is with great shock that my account was debited with such a colossal amount. My son who is 13 years old makes use of the number 27834******. When I took out this contract I told the consultant face to face that this line should not be open as I do not want any surprises out of bundle costs because I know children do not know how to manage this.

Since he had this contract this has never happened, and to my shock when my bank account got debited and went into the MTN shop they told me that this line is an open contract. I explicitly told the agent that this number will be used by my son and he said its OK. The line is a topup and you cannot occur out of bundle costs.

I refuse to pay any of these amounts as its extremely ridiculous how this is billed. Also I need an explanation as to how to get to your out of bundle charging rates.

On the one invoice I am billed R156.16 for 2.11GB of data, but on the other invoice I am billed R1269.57 for 7.38GB The amount is rand is very different calculated

I want a full refund for these amounts or I will take further steps. I have had several contracts with MTN and never have I had such bills nor out of bundle costs on any of my numbers.