exchange of goods from w big to smaller size denie

So disappointed with how u was treated in a legit store in Atteridgeville, west of Pretoria today. I purchased a body suit which I ddnt have time to fit in store. Once I got home I realized it ddnt fit me. When I went back to the store for an exchange in size I was told that they cannot accept it because they don't allow items such as bodysuits back. What surprised me was that no one told me that I had to make sure that I wasn't gonna return the item for an exchange upon purchase. The lady told me to go find someone to sell it to. When it was in the exact condition I bought it in. I ddnt even wear it down because the shirt is too big. She says its for hygiene purposes but I showed her that it's still as clean as I bought it but she got irritated and wasn't willing to help me. So not ever gonna buy anything from this store ever. I'm beyond disappoint and ddnt like the way I was spoken to.