Stuck Offline, Xbox Live Unavailable

I am unable to play this game online at all.

I was able to play it fine around a year ago, but now it refuses to work.

I have followed every single piece of advice I was able to find, and none of them worked.

My NAT Type is Open, and Xbox tells me that I have connected to the server. Despite this I am still stuck offline in-game.

Was wondering if anybody knew any different advice that could help me play the co-op campaign with my friend.