so it is connected to test socket
try quiet line test dial 17070 option 2 should be silent and best with corded phone
the most basic check when you have broadband problems is to ensure you have a dial tone and also if line silent - no noise
the best way would be to get or borrow a phone to test your line
you can always phone customer services and get engineer visit but if problem in your home wiring or setup then you will probably be charged £85 for callout there is no charge if problem outside you home which the line test would establish
There appears to be 2 cables connected to the master socket, if so the master has been wrongly wired. Any extention should connect to the faceplate.