My phone's been playing up recently, and stopped working today. It worked off the test socket at the back so I suppose it needs a new socket.
BT says it's my job to fix it, or pay them a fortune.
Question is, how long can you use the testing socket for?
Call centre says only a couple of days.

was there any cables connected to the front of the socket when you removed it ? if so it could be your internal wiring at fault if it works ok direct from the back plate.

There was 4 wires to an extension socket, but I disconnected them and it still didn't work off the front one.

This is a nice simple one for you to DIY.
I am assuming the box is an NTE5 (google it for a photo if in doubt) such that you have removed the front bottom half that connected into the test socket which you have currently plugged your phone cord into?
If so, you can purchase a new NT5 and simply leave the existing back part whilst connecting your new front part.
If you have any extension sockets wire these up to 2 & 5 only on the new front bit. Hopefully you noted the original 2/5 colours!--but no big problem.
(Whilst doing this, consider getting an "adapted NTE5" so that you can have ADSL filtered arrangements for broadband)

There is no rush to undertake the job and who will know whether you are plugged directly into the test socket?