The exact same thing happened to a friend of mine. After preordering he didn't pick the game up for a day or two, and then after that there was a whole day where the website was down. He called the store and they told him to just keep trying. After the website came back up he tried to get the code but by then it said that they were all out. To me this is total false advertising or even fraud, I really don't remember them saying anything about limited codes or anything.

To me the weirdest thing was, it's not like they were giving out tshirs or hats, or anything tangible. I couldn't wrap my head around why they would care how many people have an in-game code that costs them absolutely nothing. It dawned on me shortly later when I realized that they must have been planning on realeasing Juggernaut as payable DLC later, and maybe Microsoft balked when they found out how many preorders there were.