Sold item still on display

<p> I took a Playstation game cover "Call of duty Black Ops 3" from the display. When I got to the till to pay I was told that I cannot get the game because it has been sold already on the system although the lady had a the disc in her hand. When I complained they said there is nothing they can do. I went and took another game "need for speed", this time they told me they only have the cover they cannot find the disc. Why do you display items you don't have??</p>