Refuse to give product to client

Good day. I just had a encounter with PEP stores in Upington, Kalahari Mall. I wanted to buy a backpack that was marked down when I entered the shop. But when I wanted to puy the woman, what I think was the manager, with the name Desiré, point blank refused to give the product to me.

This is totally unexceptable!! They refuse to sell me a product that was marked down...if it was n fault from their side...not my problem. The price what the client sees it the price the client pay. I expect some feedback on this matter. Thank you