Airtel — outgoing and incoming calls expiry

Address:

Chennai, Tamil Nadu, 601202

I have been using airtel for past 10 years. Last week, i got one message regarding outgoing calls expired and need to recharge for some plans, even i have main balance of rs. 15.97. Yesterday, i have received one more message as incoming calls will expire on 13-nov, 2018. And again received same information to recharge some plans as received before.

Kindly help on this issue and provide valid reason for validity expiry.