I cannot unlock Sylvan Might, please help.

Complete a chapter to earn the right to duel a planeswalker.

This is the message I get when i try to vs Nissa Revane in the Expansion Campaign for the right to get her deck (Sylvan Might).

I have currently completed all the campaign apart from this duel, all the challenges are complete, and the revenge campaign is 100% complete.

How do you unlock this duel? There are no more chapters...

This is the closest I have found to helping me out: http://steamcommunity.com/app/213850/discussions/0/648814843...

Okay, so I was lucky enough to actually have a spare deck key to test this out, but I simply unlocked the deck by going to deck manager and purchasing all the cards which in-turn unlocked the deck for use.