Airtel — 4g sim unable to make or receive calls

I was issued an airtel 4g sim card yesterday. It got activated and the old 3g sim automatically stopped working. Since then, data and sms services have been working well enough but i am unable to make calls or receive any calls. To any incoming call, it shows that my phone is switched off and i get notified about the missed call via a sms and the outgoing calls don't even reach dial tone.
I am unable to connect to even 121.
Please do something about this asap.