Poor service

I bought a polycarbonate /awning on Sunday the 3rd at belhar branch. The item was not fit for purpose as it didn't fit properly on the door. I asked my uncle to return it, he was told they don't do cash back or refund. He was advised to take something else of the same value. For a brand as big as build it, I fail to understand why they are denying a refund. Why must I take something else worth R800 tht I don't need. I wanted the awning and thats all I needed. Now I feel like I am forced to spend R800 on something I don't need. Build it, I just want my refund. I would like you to solve this internal before I seek legal advice. I don't want to buy anything else from your store.