the master socket has one socket and we have digital voice. I’ve asked if we can have analogue and BT said no it cannot be changed
Do you have any other extension sockets apart from the new one you just added
Then no idea how the guy wired it, but obviously wrongly.
There is absolutely no need for a phone line of any description for the router to work in an extension socket. You don't need any sockets for DV, the handsets are DECT (cordless) and connect to the built in base station in the hub.
If you are on FTTC , have digital voice and only the one extension socket then to get broadband at extension you could open old style master socket and connect the wires from terminals 2&5to Terminals A&B on the back of the master backplate