Hi bobthejoiner,
Try this:-
http://www.asus.com/event/VGA/far-cry-primal/
Go to the bottom of the page and follow the instructions. If that doesn't work, you should be registered with ROG (if you followed the process above). If registered you can PM Bahz (administrator) with the following details:-
1) Country
2) Email
3) Serial
4) PPID
5) Link to picture of purchase invoice
6) List the issue/error you received while trying to redeem the code
7) The title of the game you want to redeem
Also double check that you have entered the PPID correctly.
Hope that helps.
ps you would have thought that getting a game code would be easy instead of having to jump through hoops.