Plutonium

I've been trying to connect to friends' private matches only to be met with the usual "Unable to connect to game session" in bo2 and "No available sessions were found" in bo1. I've searched around for a long time and tried to fix my strict NAT by port forwarding the 3074 UDP port. Still nothing. NAT is still set to strict and I can't join any friends. Any help would be much appreciated.