No exchange on sale items

I am totally disappointed in the level of service I got from sportscene lakeside mall.On sunday the 29th of august I made a purchase two sets of tracksuit.I realised when I got home in the evening that one of the pants was smaller.I then took the pants and slip to the shop and explained I needed a bigger size I was told I could not exchange the pants as they were on sale.Firstly if I was told this before purchasing then I wouldn’t have bought,secondly it is not in their exchange policy,lastly I did not want money back I juss needed a bigger size which is what frustrates me the most.