Sorry to hear you're all having this issue, Support should be able to look into it and let you know what it is they can and cannot do for this. Apologies for those of you who have waited a while to get help.
Got the same Problem. UBI want my Money but when you need Support and wrote UBI there is NO Help, NO Answer nothing. But please buy UBI Games and pay more than 90 and make a Membership and Pay more for my House and my 20 Cars. Hey I have no Time for Support.
YES it is a old GAME but I must pay for this GAME.
If you bought the game's DLC on Ubisoft Store you will not be helped by support to access it ever. If you bought it on Steam, it's simple. In any version of the game you have to go to the extras menu and type your DLC key so the game activates it. On steam you can see the CD key pretty easily on the game's library screen (on steam). On Uplay you have to go to the upper right zone, click on your name, Account Information/My account and then my games. CAn't understand why support doesn't give those simple steps. When you have the key go to the extras menu in the game and type it. Listo.