Airtel Data Card — Miss Commitments & bill discrepancy

i have recently taken Airtel datacard in November 2008 and that I think to be the horrible decision I made in my life.
For the first month I was in a waiver scheme but in the last/the second month I opted to be in the Rs.350/- p.m plan. The bill I received is above Rs.6000/-. I know my usage level but I think that they have Charged every second. The plan allows 500MB download free but thats a rubbish. Even the salesman are so trained that they sy thay surfing is not that chargable but thats a false. please help me out to solve the issue as the limit is beyond my capacity.the ccares attitude is also very rough and disgusting