Bsnl chennai Broadband
Huge Bill amount

I changed my plan to combo 500 where is speed is upto 2.1Mbps

I was using my connection only during night from 2.00 hrs to 8.00 hrs

my day usage for checking mail and other activity was less..

two three time my utorrent was mistakenly on and my usage touched more..

but now my bill is 4k i cann't pay that huge amount

i'm ready to pay it by installment, i don't like to cheat bsnl..

adding to this, next subsequent month bill was with 10% of previous bill amount..

can anyone give me a solution wat to do for this i'm ready to pay but not the full amount.. whom should i contact..? wat i should do .?