Did you redeem the season pass code in Exclusive Content or in PC Options –> Activate product? this is separate to an activation code.
If you did, please could you send a ticket to Technical Support so they can take a look https://support.ubi.com
I suggest opening a ticket with Technical Support so they can take a look with you https://support.ubi.com/
I didn't even know these were DLC/exclusives but where are you in the campaign game? I had 3 of themissions but 2 of them became available sometime around 2/5's of the campaign missions were completed and the 3rd didn't become available until sometime around after I completed the Key to the North mission.