Refund

I bought a Nike sports bra which was on sale for R500 in December 2023 at sportcene maponya so today I took the item back for a refund or a voucher and I was told they can refund without a slip, ohk fair enough but now I didn't buy the item for r350! I bought it for R500! NHLANHLA who I'm assume is the manager or supervisor advised they can't refund R500 cause now the item is on sale for R500...... She then gave a gift card of r350 which is the amount that the item is on sale with.... But noooooooooo I want my money..... No ways, I want my R150 back.