Multiplayer not working

I have recently changed my broadband modem & router to a Virgin Media super hub, the problem is that since the changeover multiplayer (LAN) has stopped working. I have contacted Virgin Media & they tried for 2 hours to change ports & various other ways to connect but they were unsuccessful, they have said that the problem could be with the game itself. I know that other people are having the same issues is there anyway this can be fixed?