Can we be clear about your problem. The master socket is the socket here the phone line enters the house. If you unscrew the faceplate the socket inside the master socket is usually called the test socket. Are you saying that the only place that you can get a broadband connection is the test socket inside the master socket?
If this occurred after an "electrician" changed the wiring in the master socket, clearly he has miswired it. Get him back to do it properly!