I am a prepaid Airtel mobile user. I subscribed for 99 RS monthly 3G plan on 19th of September, in which you get 300 MB data. Just like any other mobile service provider I was under the impression that Airtel too will Auto-Renew it after one month. But that didn't happen when I was shocked by continous deduction of balance, I contacted Airtel and thie customer care said that the balance of deducted because of internet usuage. I asked them that mine is a fixed plan and I never utilized even half of 300 MB limit. They simply said that 3G prepaid plan is not auto-renewable and they don't provide any facility in which they inform about this. Therefore the amount which came out to be around 150 for data usage within a week is justifiable.
Every cellular service provider in india has auto-renewable facility for their prepaid customers in 3G. But airtel doesn't and the amount of money spend within that 1 week was far more than my monthly subscription.
The biggest problem with Airtel Customer care is 90% of the people don't know english and they talk like a typical localite while chewing tobacco or PAN which is very annoying.