Unauthorised double debit

I have a contract with MTN whereby I pay around R910 a month. On the 23rd of December I was double debited, the usual amount of R900 and again two separate amounts R699 + R210. I phoned Mtn to find out what is happening and the lady told me that I authorised the debit orders. After explaining to her that I did no such thing and that I want my money back she said that she would escalate my request and the turnaround time is 48 hours. It is now 5 days later and I still have not received my money back. I have been a loyal client for 10+ years and this is how you treat me by *****ing my money. This is a huge inconvenience because I did not budget to pay Mtn double. Why the hell would I authorise a double debit? Mtn is TERRIBLE TERRIBLE TERRIBLE!!!!