Mr Price no proof of Payment no return policy sucks

I went to a Mr Price in Port Elizabeth Green Acres to return three items that were bought as a gift for my sons . Unfortunately I didn't have the till slip but I wanted to exchange for bigger sizes . I was told that they do not take returns without proof of payment , The supervisor on duty that day told me that it is impossible to change the items .They scanned the items and told me all three items were marked down to 50% less of the original pricing on the tags . These items were bought in January and in less than 3 months they were reduced to 50% and they refused to exchange for me . I had to return home with items that do not fit my kids that means I have lost . What kind of service is this when all I wanted was to get something in return to the small items i had with m e. Needless to we were very dissapointed by this service after standing in the queue for over 45 minutes only to be told we cant help you!