bsnl broadband bill —–charging more than the standard bill

mobile no of myself—9774955954
i m hving bsnl bbg combould 900 plans—-with central govt discount of 20 percent on fixed charges of 850. in this in adition to service tax the bill was supposed to be….within 760 to 761. here 2 tell that i m also nt making any extra calls more than the free calls…still i have been smsed the bill 2 pay 810.34 rs this month…..why….????