Airtel — recharge 1198 issue

Address:

Kolkata, West Bengal, 700048

I got my number recharged on 21st september with rs 1198 for unlimited calls and 2.5/day 4g internet for almost 3 months. My vendor checked this offer on my phone via an sms and i recharged. Its 19th oct today and i got a msg that my offer validity is over and i need to recharge again. Why?? Isn’t this offer for 84 days? That’s what the offer said. Why is it getting discontinued within 28 days?? I didn’t spend 1198 inr for 28 days. Kindly see to this problem. I have been a loyal airtel customer. My number is 11 years old. I don’t expect this from airtel.