Hi.
To unlock a new campaign, you must complete the current one.
I don't know if it means that you must win the last mission or every mission of the current campaign.
Then, when coming back to the menu, you'll have Cortez telling you that you can now unlock a new campaign. You must then go in the adventure menu and click on another campaign to unlock it.
I had the same issue and, on the forums, someone told me that you must get a score of 7 to unlock the next campaign, but I haven't confirmed that yet.
But there is still a bug: even getting Cortez and having a tooltip telling me to unlock a new campaign, I couldn't do so and had to re launch the game, but it worked after that.
Hope it helps