Airtel — Bill much higher than usage

Hi,
Initially when I bought a postpaid SIM ,they said it will be much cheaper than the prepaid.
they showed me the plans and according to my budget I choose the best one to cut my cost of calling.
First month they billed me around 900.I was shocked,but I paid as I had no options left.
From the next month onwards they started sending bill over 1100 Rs.I had no options left as ther was network issues in my locality.I asked the customer care and even the vendor where I bought the sim that Please change it to prepaid.They said after this week and then after 1 month and so on.
Even I paid bill of 1700 Rs.
But this month they charged me 3300 Rs bill.I am really unable to pay.I am already under money crisis and working in a private company .My family is still under huge debt.
Please do something.
[protected] was the number.

Now since I changed my network,My number is [protected].
Please consider it other wise they will again chrge late fine of some thousand Rupees.

Thanks,
Hari Suman
[protected]