I haven't unlocked the achievement for beating both campaigns, although I have beaten both(including What Ifs) and have the achievements for both of those.
I had this trouble too and its actually something weird for not getting it. You have to go and beat both final campign missions again. When the level is over, if your team has won, there is an option at the botton of the "score" screen that says "win and end campign/story". this will trgger the final cutscene for that faction and thus give you the two acheivements once youve done it for both.
To everyone else, thanks for the info...come to thin of it my final escort mission did end under odd circumstances...perhaps it gave me a score and white dot based on the fact that I finish it and didn't "win". I'll try again tonight...though I hate that one >_<...