BSNL 3G — Frequent Disconnection at night

Address:

Jalandhar, Punjab

I have a prepaid 5GB night + 1 GB day data plan by BSNL. I am using a micromax 300G USB modem to connect to the internet. During the night period BSNL keeps disconnecting me after about 10~11 mb of data volume. I use Mac os 10.6.3 or windows xp. I can't dowload any large files. I just end up wasting my time reconnecting after every few minutes.
I paid for 5GB and I want to be able to get that 5GB without being stopped in the middle.