[Q] facing problem in registering on mobile networks on one plus one topic

Actually I am here because I am facing problems in registering on any mobile network.I'm facing it since last five days and because of it I am not able to make calls use internet and It has become a majour problem. I tried rebooting many times but it shows signals at the begining but a few minutes later signals are gone and it says No Service!
Even I tried registering it manually many times but no succes !
It says 'can't register to this network at present'
I even tried deleting the apn's and rebooting the phone and then resetting them to default,even this is not working!
I didn't find anyone facing the same issue so I thought try out here, if anyone knows how to solve this problem please help!