Online appauling service

I ordered my sneakers at the Edgars online shop, i am a size 3 and its very difficult for me to get sneakers because of my shoe size. When i ordered the black and White Nike Cortez there were 3 left. So i was very excited that i will getting my sneakers. I made the order on the 30th of November and i received the parcel on the 8th with no sneakers and they say they are out of stock. What kind of stupid website that lets you place and order and pay for it when the item is out of stock. I don't understand it and i am so upset as i was looking forward to getting my sneakers, the delivery note says they will credit me for the items and they dont tell me how they are going to credit me. And when i called the call centre i was informed that my query will be escalalated to the online department, like when i pressed the prompted number i assumed i would be taken to the online department. When i went online right now at 3:49pm on the 8th of December it says there is one left. Can someone please explain to me why the delivery note says this sneaker is out of stock when i can see online and its available.