(adsbygoogle = window.adsbygoogle || []).push({});
1) Visit the Activison website and register an account and log in
2) Scroll over to the support section at the bottom of the website, which should take you to this link:
You must login or register to view this content.
3) Click "Contact Support"
4) You will then be asked to choose your console & Game - Choose this to your correct console & Game
5) Select the option "I need help with my NUK3TOWN Personalization Pack code"
6) Select the option to open a live chat
7) Write the following, but change/switch a few of the words - I purchased Black Ops 3 Standard Edition through the Amazon us/uk website which stated that I would
Receive the nuketown DLC as pre-order content, but did not receive this in the box, please could you assist me as I would like to redeem this content.

They will then ask some brief details such as your PSN ID / Xbox Live Gamertag / Steam Username
9) They will retrieve a code for you which can be redeemed and used instantly.
Hopefully this helps you guys out for the ones who bought the game used.
EDIT: this may take more than one attempt guys.