Poor service at Jet Cresta

I bought for cash a pair of men's slippers at Jet Cresta a few days before Christmas, marked at 79.95 rand. I did not keep the slip as it was supposed to be a size 8 but proved to be far too small for my son and it was a gift. On trying to change them for another different pair but of the same price, the manageress at Jet refused as the original pair bought was now marked down to 49.95 but I paid 79.95. She insisted I pay an extra 40 rand. Firstly the slippers on the shelf were not marked at 49.95 but still at 79.95 and secondly the new pair I wanted was exactly the same amount(79.95) but of a different style. Why on earth must I now pay an extra 40 rand for a change in slippers of the exact same price? No slip...it was a gift and I was not asking for a refund but a change in slippers of the exact same amount!!!They had changed the amount obviously on their system but not on the shelves. She made out because the slippers I was now taking at the same amount for what I paid, was all wrong. Please, please, sort yourself out Jet!!! I bought slippers for the above amount and I wanted an exchange for the exact same amount. I now understand why no one has any confidence in certain stores anymore. I am sitting with slippers now that are of no use to anyone in my household due to been refused an exchange. ***x