Refusal to Refund

I was charged for the same item of clothing twice. The sales assistant said that the payment did not register on her port even though the slip showed that it was approved. I confirmed that they would refund me if the funds reflected on their side (twice) The refused to refund me. I requested assistance from my bank as it was a duplicate payment. They informed my bank that they couldn't reverse the payment. The manager at the shop said she could not refund me. I understand that mistakes can happen but their unwillingness to rectify THEIR mistake is what upsets me. I have been inconvenienced repeatedly and now they inform my bank that I have to go back to shop again... for what. Just so they can inform me that they still can refund me. Am I just to accept that I have to pay R 1000 for an item of clothing that cost R 500.00. Their service, or lack thereof is a disgrace. I will not recommend Fochini Mokopane to anyone.