Airtel Broadband Connection — internet biill

sir
i have an airtel broaband connection my present plan is 1099. in sep 2009 changed my plan to 745 and my bill was Rs7500.i was complained to airtel office that the summary received about the internet usage is wrong.after that they commit to pay Rs2600 for the month.but after 2 days of payment my connection was terminated and airtel costumer care call me and told me that your unbilled amount of Rs1426 is remaining.after a small conversation with they commit that to pay Rs1000 and remaining Rs426 is less from your next month billing amount.but my present billing amount is Rs1869(including disconnection charges and previous balance).first they committed to me that less the remaining balance but at last include the money band also charge for disconnection.this is not fair.
so i requested to you that please solve this problem.