Refund on my credit card

I went to shop at Checkers Forest hill on a Saturday 2 weeks ago and when I was at the till I used my Fnb credit card to pay for the grocery I swiped 2 times and it declined then I use a Nedbank card and it was approved then when I ask them what was wrong they say fnb was off line ,then after 30 minutes I receive a massages on my cellphone indicating that the transaction has been made at checkers on my credit card then I went back to ask for my refund they told me that I must bring a bank statement and unfortunately the banks were closed then I went back on a Monday and they told me that they will call their head office to refund me but since then I never receive my refund I NEED MY REFUND BACK .