Port Forwarding

I have successfully port forwarded many routers on Cox Internet. Currently I have tried setting up a Buffalo WHR-300 HP dd-wrt router with the same settings that have previously worked. When I use a port checking website, I have tried several, I find that no ports are opened. I have tried different routers, another brand new WHR-300, a Buffalo WZR-300 that I have successfully port forwarded on a previous project and a D-Link router that has also successfully been used to port forward at another job site. I have tried 2 different computers at 2 different Cox network locations, the job site and my network at home. All to no avail.

I have verified my router set-up with a colleague who is currently successfully port forwarding on his network with the same router I am attempting to use. I have turned off my firewall  and my anti virus. Again with no success.  Cox tier tech  support cannot or will not help me. Their official position is they do not support port forwarding, if it doesn't work it can't possibly have anything to do with their network.

Has anyone out there got any suggestions?