Airtel — sim not registering to network

My airtel 4g sim seems to not be able to register to "ind airtel" network and so, my mobile shows that it has no data sim, while on searching networks, "ind airtel" is one of them, as mentioned above.

This has carried on for 3 days now, while i have been using this sim for 2 years.

I have tried switching signal type to 3g, and also all the other trivial solutions, still any kind of help will be appreciated.