Airtel — airtel sim card - no service

Website:

www.airtel.in

All of sudden the airtel mobile network got cut off and shows no service on iphone5s today.

No use even after:
- device restart
- network settings reset

When sim card is removed, it shows no sim but when it's inserted back, it shows searching for a short time and then turns no service!
It clearly indicates the network issue!!!

This is very critical as the entire network is lost for me for the complete day and i could not make/receive any urgent calls and other network services.