It just rings once and then drops the line
If you can borrow another phone to try (from a friend, family member, neighbour) you could try swapping the phone to confirm the fault is on the line if you feel like doing any further investigation yourself. Otherwise, your description sounds like a 'ring trip' kind of fault. One of the VM forum team will reply here within a day or two and will assist you in fixing it.
Thanks for your post on our Community Forums, and a very warm welcome to you @Drowzzee.
Sorry to hear of the issues with the landline services.
Can you please advise me if you've been able to try an alternative handset in the master socket?
Do you have any pieces of equipment attached to any of the extension sockets?