Issue exchanging an item

On Friday the 15/04/2016 we went to exchange to clothing items.We handed over the items and the slip as requested the refunded the money to a gift card as we were told it the standard procedure. We located the items the EXACT same items that we originally bought but one size larger. The one pair of pants we noticed was R270-00 instead of the R250 we of the original item. Suddenly the tills we were short R200, we retrieved the slip to realise that the R250-00 pants had gone through at exactly R125-00 half the value the lady said it was a special most likely. I asked to speak to a manager she called the receiving manager who said it was head office's pricing and was basically a mistake. My mother said that she did not notice when it went through and thought she paid R250. I told the manager it is an exchange and that we would pay the R20 difference but not the R200 as i don't see how a glitch is our fault, he said that is was my mother's fault for not noticing and they would do nothing, I phoned the call centre and got the same response, I put the phone down in the lady' ear I was upset. I understand we got a bargain but if this is Pick n Pay's attitude we will not be returning.