Refusal to pay the price on display for Sheraton bedding

I went in to buy a Sheraton king size duvet cover set. The prices I saw was R499 and R699. I took the king size I was looking for. When I pay it was R799. I asked why it was a different price from what I saw. The cashier went and took another bedding who maas R499. I paid for mine. Before i left, she called the floor assistant to come and fix the prices as they were wrong. I asked to pay mine for the price I saw. The called a manager who told me that it was my respite check the bar code of the iterm I want to buy. I felt that it was unfair to pay the price that was not displayed. I demanded that they refund me the difference as it was their fault to display wrong things and they refused