Unhappy customer

Horrible service from the Tekkie town at Brits Mall. The staff and manager was so rude, shouted at us, was unwilling to help and provided us with incorrect information. I purchased a shoe for R899 and needed to exchange it for another shoe, however on the day we went to exchange the shoe they was having a 20% sale on certain items. I picked a difference shoe for for R1000 and with the discounted price it came to R800 (so in other words we should have gotten R100 back), however the salesman told us that in order to get the discounted price we have to open an account so we said okay. Then after he did the exchange and everything when through he tells us that because we opened the account the shoe that we originally purchased for R899 (which we paid cash for) will also be discounted so we can't get the R100 refund. I still do not understand how that makes sense...