Have you called the broadband team?
NOW Broadband Members can call us 8am–8pm, 7 days a week.
Was there something missing in the NOW Hub box packing?
There is only a couple of items included which from memory are :-
1 × NOW Hub Router.
1 × Power adapter with connected power cable.
1 × grey DSL cable with one end with a purple plug on it.
1 or 2 × Micro Filters.
Do you have all the above accessories?
If so then if the Engineer has already fitted the BT master telephone socket plug in the NOW Router just to see if it lights up the three green lights on the front of the NOW Router anyway (give it around and hour or so).
Here's some instructions with regards to a self install of the NOW Hub 2 Router.
Could have meant Ethernet cable , if connecting to a laptop, or other device.
Used to check line stats speeds etc, as opposed to wifi which can be prone to issues, and doesn't always give a full picture.plus you don't need passwords etc for ethernet
I am surprised if the Now routers don't come with an ethernet cable. Every ISP router I've had has always come with one. There is also no reason for the installer to want one, but they will want the DSL cable if they connect the router for you.