This issue is usually attributed to the sim card not communicating with the network.
You may need to ask your network to carry out a sim swap which moves your tariff and mobile number to a new blank sim card @ManjuRacha
As a process of elimination try your sim card in another phone and another sim card in your phone.
You could also reset your network settings to see if that helps.
The steps to doing this are.....
I wish you all the best with this situation.
Daily Driver > Samsung Galaxy s²² Ultra 256Gb in Phantom Black.
The advice I offer is my own and does not represent Samsung’s position.
I have no affiliation with Samsung.