try to get hold of person managing the broadband at your exchange and call them directly. person at my exchange is very nice, usually corrects and calls to verify in 1 hour of "informal" complaint.
but the ones in the phone dir didnt work. the first number was outright denied to be a BSNL no :S , second one went to elsewhere in the city . that guy was couteous , and gave me w no , which strangely didnt work :|