Airtel — outgoing call disconnected though have main balance

Address:

Bangalore, Karnataka, 560016

From 12th dec outgoing call disconnected on mobile though have 200 rupees balance on main account. Got message as need to recharge with 23 rs to reactivate. Not understand what is the use of main balance?
I heard as per new rules if there is a main balance out going calls should not disconnect, not sure if there is any other terms and conditions included. Please help in resolving this issue.