Bundle account charged more than agreed

I have a data package of R130 per month which was capped when I reached the usage associated with the contract. The sim is in my 6 year old's ipad. All cellular data has been switched off, I have Telkom ADSL at home where we use the WiFi. I have also personally been in to MTN store Somerset Mall to confirm that the account can not go over the contract amount, and the sales person guaranteed me that it will not be charged more. This morning I had a deduction of R4083 for MTN from my account. I phoned MTN customer service and after staying on the line for 16 minutes, have not been put thru to a single person to talk to!!