The Division Underground DLC is out and has had many reports from people saying they can’t find it despite paying for the new content.
The Division Twitter account has said that Ubisoft now know of the issue, and it has already been resolved for PC. Advice has been given on what to do if you’re still encountering problems: on Xbox One, if you have the Season Pass, you need to unlock the DLC in the in-game store. "Click purchase and the game will detect that you own the season pass."
If you’re on PC, you can restart Uplay. On all platforms, if Underground is shown as "offline," you need to make sure you complete the Secure Quarantine Center side mission which is shown on your map.
The Division has suffered many technical issues and severe backlash after a less than perfect launch and the game has now received many patches to resolve ongoing issues.