This is not what I'd expect because this isn't the specs of the plan: in your circle, I can see the plan you're talking about, which is:
Pack Type: Sachet
Maximum Service Charge
Prepaid: Rs.11
Postpaid: -
Plan Benefit: 30 min
Validity: 1 day
Bill Shield Value (Postpaid only): NA
Charges Post consumption of Plan data benefit (reset every recharge): Rs 3/min
Charges Post consumption of Plan data benefit (reset every every bill cycle): NA
(Sorry about the bad formatting - see
3G Tariff Plans, Best 3G Plans, airtel Internet 3G Packs)
In other words, you'll get ticked for Rs3/min when you continue using the service. AFAIK the only one that does what you're proposing is some Rs675 which is a data-based plan (they call it "FlexiShield") - it gives 3GB to start then the rest of the time on GPRS/EDGE. It seems they are implementing this on their standard packs as well according to the page for your circle, but yeah.
That being said, I would agree with your sentiments - they *should* simply terminate the session or auto-renew the 30 minutes pack if your session is still active - which over the space of 2 hours would have saved you about Rs950, but, in 2 hours the deduction *should* have been ~Rs360, not nearly Rs1000 as you claim, so...