Refund on shoes

Bought R4000 worth of shoes at tekkie town river Square. My sons shoes didn't fit, and while he put them on, ge got a small dirty mark on top of the shoe. I didn't see until we got there and then they refused to refund or exchange me. I then asked if I can just remove the mark and then come back. They said no... it was really a small mark, and the shoes are still in perfect condition as they weren't worn! Now I must throw R900 down the drain. But no one complained when I spend R4000 there!