Refusing to refund an unauthorised debit

On 25 November 2015 debit order was taken for a loan arrangement and again on 12 December 2015. The arrangement date is 25th of every month, yet Saturday when I went to the silverton branch they refused to refund my money as they said an investigation needs to be done. Why would an investigation need to be done if the debit order was not supposed to be taken??? a very clear instruction. I need my money to be refunded today or I will have my family close their accounts at capitec today still!!