Sounds like the ISP or the apartment management is restricting access to FF14's servers, likely the latter.
In order to bypass that restriction, you will need to connect with the VPN and use it all the time while connected to the FF14 servers.
You can also inquire if the ISP or apartment management is blocking FF14's servers or the ports needed to connect to the servers:
  • [Ports that may be used] TCP：80, 443, 54992～54994, 55006～55007, 55021～55040