Mtnl 3g data card not a jadoo

I recharged my net with rs. 5000 on 14/2/12 and it just worked satisfactorily for about 1 month and after that whenever I want to download anything it gets disconnected time and time again displaying a msg that ur balance is low plz recharge by dialing 400. But this is not possible. My balance cannot be so less so early. Whenever I run any video on youtube it takes hours to download just a one minute video. When I try to download for example a 5mb file if it gets downloaded upto 4.9mb it gets disconnected. I get vry angry every time. It irritates me vry much. But the problem has increased now it cannot even open google homepage now. What is its solution?