Airtel — reactivation of #[protected]

I had last used the number #[protected] in april or may. It was a sim with lifetime membership. All of a sudden i have found that the number has been deactivated. Please guide me through to reactivate the sim. This is totally unfair and how can a number get deactivated when it was used just 3 or 4 months back without being brought into the notice of the person using it!!!

Regards,