Airtel — recharge discrepancy

My mobile number is [protected] wherein last time i recharged with offer amount of rs 98 for 28 days which expired on 23.04.2018. Previous to that i was getting an offer message of rs 99 for 28 days. Accordingly on 24th i recharged for rs 99 but i got a message stating that the validity only for 10 days. How it is happening and it is merely antognizing the existing customer and misguiding the patronage customer. Kindly correct the validity to 28 days and confirm