Ah, things become a lot clearer. Thank you.
So, as I understand it, you have a VDSL2 service at your place of work that makes use of the inbuilt VDSL2 modem of the DGND3700.
As I no nothing about your IoM ISP (or how its VDSL2 services are configured) nor the Netgear DGND3700, the best advice that I can give is to take note of the configuration settings of the DGND3700 (when it is in use as a combined modem/router device) and configure the
HG612 accordingly.
I realise that is not much help and is, really, the obvious . . .
Perhaps you would like to show us the configuration settings of the Netgear DGND3700, when its VDSL2 modem is used? That might provide sufficient inspiration as to the adjustments required for the
HG612.