Overcharged and not being refunded - Absolutely useless customer service

I was overcharged by Mtn supersonic by almost R1000 at the beginning of October 21. I contacted them straight away and explained what had happened, they saw the problem on their side, gave me a case number and told me supersonic refunds would be processed on Fridays. I waited a few days after the first Friday and still I had not received the refund owed to me, I contacted Supersonic again and gave them my case number which they said did not exist so I went forth to explain my problem again, this time being told that a refund will take 21 days to process. (Hope They gonna pay interest on my money). It has now been past many Fridays (when they supposedly process refund) and well over 21 days and i still have not even heard a whisper from these people no email nothing! Can I add there customer service teams english is absolutely horrible as well. Would 100% not recommend the service provider