Inflated Data Bundle Charges not what I signed up

I am totally perturbed at the huge amount that was debited to me today , R7080. my monthly debit order for 3 contracts is generally R1700... how MTN how do you come up with this crazy bill. Upon calling your call centre this morning they are unable to provide any answers all I get is you will receive an email with details. Simply not good enough. You charge me this massive amount I want an investigation done on my billing and account with you . Surely after been a client after 20 years with a sterling track record who never deviates from her monthly usage on cell package , now out of the blue to get ********** by you. Totally insane right. Two of the contracts are for my kids which are top ups so please tell me how does the one bill go up to R4999. There are limits on this for a reason . You have messed up big time MTN , I am taking this to ICASA and also reversing this debit order. If you cant get your data issues sorted out I shouldn't have to take the brunt of it. This is **************** ....I will see this to the end, this is theft MTN!!!!