Replacing the socket didnt fix anything. Just more NPC's blindly following their lists instead of observing reality.
Also I dont use a landline phone.
I posted a solution. Hope it saves fellow brits from dealing with incompetent support.
You asked if anyone had an opinion as to what was going on and I was only trying to help come up with a real solution instead of a lash-up. I freely admitted I'm not a telecoms engineer.
I know you said you don't use a phone but just out of interest, are there any old extensions connected to that master socket?