Finally the problem is solved today. Thanks everyone for your suggestions.
Actually I mistakenly subscribed Sadabahar Hits (Ch 194) service in my account. After that "Airtel FTA Bundles ROI" pack was removed from my account. Tried to fix it with Airtel thanks app, message system and Customer care service, but nothing happened. Yesterday I sent an email to airtel and got response from them. Today they talked with me by calling to my registered mobile number and removed Sadabahar Hits channel after my request. After removal of the service channel now all problems has been solved. Through Airtel thanks app i added the Airtel FTA Bundles ROI pack and now getting all FTA channels in my account.
I think Airtel's customer care service is not bad...!