Airtel DSL — Excessive billing unresponsive

My landline no. in Delhi, recd. an exorbitant bill of Rs. 3000+, while I usually get around Rs.[protected].

I emailed to Airtel to:
1. changeover my plan to lower one immediately. I checked the plan options from their website. Later I got a reply that, that specific plan did not exist.
I then suggested another plan. When I opted for that plan, they dilly-dallied for 7 days, and have now called to say they will change it in another 48 hours. THUS THEY MADE SURE THAT THEY WILLFLEECE ME FOR ADDITIONAL 10 DAYS.

2. I asked them to looked in to the high bill amount. On this they never reverted; but made sure to call me to remind me to pay the bill.

they always call up subscribers about upgrades - but never inform about newer/friendlier plans.