Airtel — Airtel sim not able to connect to network

From past 2 days my Airtel Postpaid number is not able to connect to network tried various mobiles as well. Tried all the possible way to sort the issue but none of it worked. Contacted Airtel support they say sim has issues needs to be replaced but the thing is how come a sim that was working for more than 4 years suddenly got this issue. I asked to have it delivered in Covid-19 times and they I have to visit to Airtel office only to have the sim delivered and the place I am currently at has no Airtel office for more than 100km. How am I supposed to enable the number this is causing me huge problems