Bsnl 500c
Less speed at night

I have been using bsnl broadband (500c plan) since 20 months, generally i use to get speeds of 1.6-1.9Mbps (200-230 KBps) always.

but for the past two weeks at night unlimited time (i.e., from 2-8 am) i am getting very low speeds of 70-180Kbps (9-20 KBps), is BSNL deliberately doing this, if it is then its really disgusting.

is anyone having the same problem?