Impossible to get a refund!

On 2 December 2015, I overpaid my account with MTN. I should have paid R69,64 and instead paid R6 964,00. Unfortunately the bank couldn't reverse the transaction, so I was left to deal with MTN. I provided all the information to customer services telephonically with no joy. I then emailed customer services and was told on 7 December to send the proof of payment, which i immediately did. Since then I have followed up by email no fewer than eight times with little joy. The latest response on Monday 28 December was asking for my full bank statements which I immediately sent. On following up again on Tuesday 29 December I was asked once again for the bank statements. After sending the documents again, I was told the refund will take 7 working days. This will mean the resolution will have taken longer than a month! Given the communication history over the past month, I'm not convinced.