Airtel — outgoing call facility blocked by the service provider

Address:

743252

My account has balance of about rs 16. But since it is not recharged for more than a months period, out going calls are blocked and also incoming will be blocked very soon. Portal shows validity for sim ([protected]) as unlimited.
I read in paper that telecom service provider cannot stop service if balance is available.
This number belongs to my mother for home used and normally its recharged has done asusal it's need.
Thank you