Plutonium

For the past two weeks, my friend and I have been trying to join each other on Black Ops 2 but have been unable to.
We have tried restarting the game, reinstalling, checking if it was allowed through the firewall, updating steam, closing steam entirely, and port forwarding but nothing has worked.
We used to join each other just fine till one day it stopped working. If it matters, my friend is in Germany and I'm in the U.S. any help would be appreciated