any idea where i can download it?
If you had purchased the unit from BSNL, they will replace it,
or give some other modem+wifirouter
If on rent no problem. they will exchange it.
Firmware update is risky and you may have a "dead" unit.
Probably the SW version will be what is available
In WIKI herein this forum. confirm.
Software Version: 3.12L.01.A2pB023k.d20k_rc2