Denied Doscount

I opened an Edgar's account at Sandton, I was told I have a first purchase 50% discount on the card, and had to buy today. I took two shirts and two Chinos after ~2hrs of browsing and fitting. When I got to the till I was told I can't use the 50% discount on those items because they have discounts also. I told them to cancel them and give me the 50% but they refused and said I should go back and take something else or lose the discount, meaning going through the long process of looking for non-discounted clothes through a packed shop. I ended up giving up the discount and took the clothes with a price I did not plan to. This was unfair and it was not right. I am upset and I feel like I was ******. Had I been told in the first place that the discount applies only to non-discounted clothes...