Check your emails carefully again, I thought I didn't get one either, but it just turned out that the serial number was printed above the registration instruction, so I just completely missed it. I had to check through the email a couple to times before I saw it.
Either way, if you are sure you did not receive a serial, just know that this forum is full of people who have already bought and registered their game, so there is clearly something wrong with your order and your problem will be fixed eventually.
I'm not an employee or anything, but just keep looking into the problem and hopefully something will be done.