A long shot, but ...
Has your modem got two sockets in it -- one for the phone line in and one for a phone out (so you don't have to use a 2-way adapter in the phone socket)? If so, have you plugged the incoming phone line into the correct socket?
What is ransomware and how do I protect my PC from WannaCry?
What I learned from my mentor, Oscar-winning VFX supervisor Phil Tippett
Siri vs Google Assistant
Synology invites you to visit them at Insomnia on 26th – 29th August. Book your tickets now and visit Synology.