Airtel — sim deactivated no lost

Address:

Lucknow, Uttar Pradesh, 226003

I own a airtel prepaid sim of lucknow circle but suddenly the sim got deactivated, i went to airtel store and they told me that the no has been discontinued, when i asked why tgey said the dont know the reason. Its is a very old no of mine and loosing it will hit me with big loss. I need to know why my no got deactivated how do i recover that. Presently im in delhi when ever i call the custoner service they say they cannot help... Kindly help