Bad Service at Malmesbury Mr. Prize

I Brought a Short Pants at Mr. Price Malmesbury a day before Christmas at the time the Shop was full and overloaded with People so me and my wife were standing in the queue while we were standing lady come to us and ask us if we want to pay by Card we sad Yes that will spear us very much time and then we went home not directly but after an hour or so got home the Pants were to small right the Next day after Christmas we went back to get a bigger size so the Shop assistant said that we can return the pants without a slip we had the slip but it was all white because of the swet and wetness but my question is a shop like that is suppose to just return it or give a bigger size or the same amount the pants cost for the same prise know they wants us to wait until the promotion is over and then retun it you know how much petrol i must drove for R100 PANTS. very Pathetic i will not buy at Mr. Prs even if its the last shop open