Delay in getting a refund from Travelstart and Mango airlines.

I made a flight booking through Travelstart for a Mango flight. Although i only received one booking confirmation for the flight, there had been a double booking on the side of Travelstart which led to a duplicate debit on my credit card. I contacted them on the 4th of September and after numerous phone calls telling me that they have referred the matter to Mango I resorted to contracting Mango airlines directly on 21 September . Mango initially informed me that they did not receive any refund request from Travelstart. I have just made my 5th call to the Mango refunds department and have had yet another call centre agent tell me that they are still investigating the issue.