A sorry story but one which is oft-repeated on here. Regarding your mother's phone extension, that should be completed free of charge as part of the switchover process (linking the phone socket on the back of the hub to an existing extension or providing one in the required location). See
https://www.virginmedia.com/help/home-phone/virginphone/switchover
You’ll need to book a free technician visit if:
You’ve got connected devices such as a burglar alarm linked to a control centre, use a telecare device, or have other phones connected to extension sockets. You’ll need to contact your provider and let them know about the switch if you have any of these to make sure they’re compatible with a fibre service
Your Hub and phone can’t be placed near each other
The part where this often seems to go wrong is making sure the VM technician has enough time to do the work and is aware it needs doing as part of the switchover. On some past topics the switchover has happened first then the extension work has followed as a separate visit.
There could possibly be some genuine reason a connection to the hall might not be possible but I would guess the VM tech wasn't expecting to do this (or possibly didn't know how or have the right parts) and has just come up with his own excuse in order to leave.
You have taken all the right steps to have the work done but it has been bungled by the VM system/phone support in not booking the work properly.
Hopefully the VM forum team can rescue this for you and sort out the connection of the extension socket for your mother. Someone should reply here within a day or two.