Unable to return sale items

first of all the amount of attitude received from the manager at Ottery Hypermarket was so rude and disrespectful. She wasnt interested in helping me at all. My sister-in law bought a sale item for my baby which was too small. She's out of the country so I had no tillslip. I was looking for no refund merely to exchange the item for a bigger size. unfortunately after searching in a number of stores I could find no size for my son. After explaining this to the manager of the clothing department she said they dont exchange sale items without a till slip which I can understand but after explaining that I couldnt find the item anywhere she abruptly told me that there was nothing she could do. I wasnt asking for money back or even for a item of higher value. I merely wanted to exchange it for sumting else. I then went on to ask whether she could try and check if any store had a replacement for me her only response was sorry we cant help you. I do all my shopping at this store and I have never felt so disrespected and brushed off in my life. I then asked so what am I suppose to do her response to me was: you need to go to all the stores and find 1. Wow really if this was any other store ie: foschini , woolworths edgars ackermans even they would have taken the time to atleast help me source the items after I specifically told her that I couldnt find it anywhere.