Airtel — Airtel cheated for no good reason

Recently i recharged my airtel mobile number with a plan of rs 129 that should provide me with benefits for 28 days. I got benefits for just 20 days even though it's showing recharge successful.
Airtel being such a good company too has these bugs in there system, shocked but true and also sad at the same time.
Has airtel started cheating for these small small amount?
For this 129, i have wasted my nearly 10-12 hours on customer care, where no one responds.