Airtel — Mobile network not available on airtel sim card from last 4 to 5 days

From 3-4 days, all of a sudden my airtel sim shows no network while on other airtel sim working totally fine. After several tries like rebooting, changing the phone, and restarting there was no improvement. I also went to a nearby airtel store they offer to change issue the sim card with the same no. but still, there was no signal it is still showing no network registered.