Order online sneaker empire SA

I enquired about a sneaker and size which Sneaker Empire SA confirm that they have stock and size and was qouted 1900 incl delivery which I paid for. I had to follow and only discovered they don't have the size7 and forcing me to buy something else. Why agree about the make and size in the first place knowing they don't have size. I want my refund which they refuse to do. I'm annoyed and frustrated.