Incorrect amount charged and poor after sales service

I rented a car from Avis in South Africa. They charged an amount incorrectly on my card. Instead of charging the amount in Rand they charged the exact same amount in UAE Dirham which is four times more at the current exchange rate. The manager that evening admitted that it was a mistake and said that they would refund the extra amount asap. As per my bank I haven`t received a refund till date. I emailed Avis more than 6 times starting from 18 Aug. I am only asking for a statement on my account that reflects the amount that they charged, the amount owed and the deposit refunded. I am only getting generic emails back and nowhere nearer to sorting this small issue out.