Not recieving incoming calls outside of the office network?

Question

My office uses barracuda cudatel as our sip provider.  When I set it up, everything works fine at my office.  Whenever I am outside of my office network, I don't receive incoming calls but I can still plce outgoing calls. I have whitelisted it on my firewall but the problem still persists.  

Any feedback on how to fix this would be greatly appreciated.