Airtel — Sim card not working from past 2 month

I am using airtel sim card since july 2016 which i got it from ( bannerghata airtel store ) from last 2 months i am not getting network in that sim card for that i visited near by airtel store to rectify my problem they told me after checking in their system that this sim card is registered with some XYZ company . some fraud had happened with me how is t possible that the sim which i am using from past 4 years is registered with some company name . i have sent sevral mails to airtel customer care but i did'nt get any response . please look into this otherwise i have to report a FRI regarding this because i have been using this number for my official purpose .