I am sorry to hear that you have been unable to connect. Please provide me with the following info:
Which platform are you on? Are you using a wired or a wireless connection? Where you able to connect before with no problem? Can you tell me your NAT type?
You should be able to see your NAT type by going to the multiplayer menu and selecting "Play Online". From there, check the bottom right of your screen and it should have your NAT status listed there. Have you tried connecting directly to your router and playing online through that way? Are you receiving any kind of message when you tried to play online?