ridicilous amounts withdrawn

On the 2nd of January 2015 an amount of 17000 was withdrawn from my cheque account. I rushed to Std bank Randfontein to have it reversed. It was reversed but resulted in me being in a negative balance due to the amount. I had to do a job on that Saturday but the client cancelled the job due to me being unable to supply.THe deduction shows ats MTN SP. I asked the consultant to totally block this as I have never had an account with MTN. How can Std bank allow any debit orders or deductions from my account if I did not give any written or verbal consent. I have given this through to the MTN ***** department but no feedback yet. Whats very funny to me is that the end of November last year I went to settle a revolving credit loan, paying from my own cheque account, but the bank had to first confirm where the money came from.I just got a sms that an even bigger amount was deducted this morning.This is really frustrating as I now have to leave everything and rush to the bank again, at the endd of the day who is responsible for this costs.