Airtel — carrier registration failed

My phone doesn't shows any signal and I cannot call to 121 also I am facing this issue more than 4 hrs it is not registering to the network it says error I can't call message and no internet please fix this issue
What can I do now please tell me to fix this
After my system update only it seems like this before that there is no problem

Any way please fix this issue

Lots of people are also suffering from this

It is one of the leading network provider but it is not talking care to their subscribers