My FaceTime is not working since I upgrade to os capitan

hi I recently upgrade my MacBook to new OS CAPITAN now im having hard time with it as my FaceTime is not working anymore as it use to work on Yosemite it was perfectly fine on that Os I live in Dubai I know it's blocked here but I use VPN and it works fine but now I'm not sure it's only me or it's an os defect I've seen few post regarding same issue I don't know how to fix that I did everything i reinstall the same Os twice but still it's says either call failed or the people calling is unavailable

if you having same issue and got some solution kindly share thanks