Cross trainer doesn’t want to refund

I purchased a nike jacket for R1299 in a medium size on the 26th June 2019, today I went to going and change it for a smaller size and they advised me that they dont have a small, I asked them to check the other stores and was advised that they also don’t harbor any smaller sizes, I asked for a refund and was told that they don’t offer refunds and they can provide me with a gift voucher, I then asked them if all your stores don’t have my size what will I be buying with the gift voucher, I then called head office and complained that they did not want to refund my money and got the same response from them, I feel that it is my right as a south African to demand a refund for a brand new product that wasn’t worn especially when the store could not provide the product in my size, when I asked about the CPA they told me that their rules trump the CPA if they advise the customer before purchasing which I feel is a dirty trick for such a huge brand trying to force me to spend my money at one of their stores even though they don’t have the products that I want