FTB Server Friends can't connect
I don't know what you did exactly to activate port forwarding but my guess is that the description you used does not mention that some routers have an internal firewall too where you have to open the port aswell.
In addition to that, you might need to open the port in your local (PC) firewall too.
(This might also be the case if you use a VPN, like Hamachi which was already mentioned by Flaunting.)