Store refuses to exchange exact item as originally bought

I bought clothes for me family on the 06th January 2022 using my Mr Price Account. 3 days later I gave my sister the original receipt to go and exchange one item of clothing and the store refused to exchange for her even after she gave them the original receipt ad it states on the receipt and website as well as a letter from me. The Store manager Called Rose insisted that even if she keeps those clothes for a year as long as it's not Mr exchanging she will never exchange. what's the point of having ur website return policy and receipt return policy if you store does not abide by it.