Airtel — airtel's sim is not working since 10 days

Address:

Etawah, Uttar Pradesh, 206001

I have 2 airtel's sim but one of those sim is not working since 4 days i contacted to airtel's so-called customer care services via calls & emails too but i don't get any specific and accurate answer regarding my issue. They are continuously tolding me that your "sim card is gone old upgrade it to 4g network from any airtel's store or any of the retailer without any charges it means absolutely free" but when i went to an airtel's store or to any retailer all are asking for ₹100 to upgrade my airtel sim card to 4g network. But still the airtel is still avoiding my issues.