I'm assuming you got either the hardened edition or the care package edition. Those are the only 2 that include Nuketown Zombies.
The regular edition only has Nuketown 2025 if you pre-ordered.
Did you redeem the Nuketown 2025 code, or the Nuketown 2025 ZOMBIES code?
2 seperate things...
Nuketown Zombies will be released with the first DLC drop for Season Pass Holders. So if you have a Season Pass then you are set and if not you can purchase one for about $50 and get Nuketown Zombies and the 4 preplanned DLC drops.