My observation. This Rs399 plan is appearing every alternative day in the airtel app. If you dint not get today, you will get it tomorrow. Yesterday got in my primary number and dint get in secondary num. today its just opposite.
Today I have received SMS from Airtel
Effective 14 Apr 2017, benefit on Rs 399 recharge for Airtel mobile has been revised. You get: Unlimited Local+STD Calls+ 70 GB (1GB/day) (on 4G H/S+4G SIM) Validity: 70 days. (T&C Apply)