Its not the socket itself, its any wiring that may be still be connected to the phone line, as this will upset the broadband.
Where there any wires connected to the point shown on my last picture?
If there were no wires there, then you need to find the other end of the wiring that goes to that upstairs socket, and make sure its disconnected from your phone line, as it may bee teed in somewhere else, as shown in this diagram.
The picture shows a filtered socket, but the principle is the same, no other wires connected.
No wires connect to the back of the faceplate of the master socket, suppose I need to see if the socket comes outside of the house and trace it?
Yes, as it can be the cause of dropouts and loss of speed. Its not unusual to find wires teed into other connection points, especially on older installations.
And if it connects back to my phone line I need to contact BT to resolve it? Would this come under Early Life Failure
If you cannot easily disconnect it, and you are still having problems with speed and dropouts, then when Openreach visit, you can ask them to disconnect the unwanted wiring.
I would leave it to them do deal with it.
If they are observant, they should be able to see that for themselves.
Your current issue would be an Early Life Failure.
Do you want me to ask a moderator to arrange a visit, or are you going to contact BT directly?
Please could you ask a moderator that arrange an engineer visit and confirm that it would be chargeable as its Eary life failure?
I have asked a moderator to provide assistance, they will post an invite on this thread.
They are the only BT employees on this forum, and are based in the UK.
It may be tomorrow morning when you get a reply, as they may have finished for this evening.