Selling goods out of stock

I needed to buy grey Roman roof tiles. The sales lady at the New Market store said there was no stock of Grey but she had Terracotta. I bought the terracotta tiles on my business card and went to the loading area. When I was there they had no stock and only had red. I then had to return back to the store where I was told by a different salesman that there was no stock at all. After arguing about how they could sell me something that there is no stock of I had to go to another checkout point and do the whole refund process and they changed it to red tiles. Then they requested I had to pay a R5 difference which unfortunately don't carry cash on person and refused to swipe my card. Another customer actually gave me R5 to complete my purchase. This took 30 minutes out of my day which is completely unnecessary. Not impressed with Builders New Market.