BSNL 1350 broadband plan
The internet gets disconnected in a few minitues by itself

I have been using BSNL broadband plan from almost 5 years now. But recently from a few moths i am facing alot of problems to get connected to the internet. Its like in in few minutes it gets disconnected by itself and even if i go to 192.168.1.1 and reset the modem its of no use. It take a few minutes for the internet to come back. I am using Windows 7 from almost 6 months now and i have also complained several times in the BSNL office (in ever week atleast i call them up once to come are resolve this issue) but it all has gone in wain.

Can some one help me out and tell me a solution to resolve the same.