Hi T_W,
Welcome to our community and thanks for posting. Sorry to hear that you're having issues with your landline, we appreciate how frustrating this can be especially when its not working as it should do.
As we will need to do process of elimination first can we ask if you have tried another handset in the master socket? Also if you have any extension sockets please can you make sure these are all unplugged and you just try the main handset in the master socket.
Please can you try the above first and if you still require assistance please come back to us so we can hep you further.
Kind regards Jodi