Sanral - Refusal to pay money back

On the 9 th of July money owed to me was wrongly paid into the Sanral account. Upon realizing it I lodge a complaint with Sanral. Every time that I call they issue me with another reference no and nothing further happens. They requested that I supply them with a bank statement with the bank logo on, which I did. If I now send an enquiry they just cancel it. I just don't know what to do to get my R6000-00 back. It must surely reflect on their books. If I do not get feedback by Friday I will open a case of theft against SANRAL