What have you tried to do to get it to work? New OS, settings changes on the router, etc?
Having to clone the MAC sounds strange. What type of broadband connection do you have and why did you try cloning the MAC? There might be MAC filtering on, in which case, just add the phone's MAC as an allowed device in the router's settings.
Try a VOIP test. That'll show that your connection at least has good enough quality.
MySpeed VoIP connection test, VoIP test, test VoIP performance, test VoIP quality
It sounds like there's something preventing your phone's pcakets from getting through to the network. So some kind of filtering on the router or the network.
Anyway, give us some more info on what you've tried and someone should be able to help. Otherwise we just have to guess.