Why do I have no telephony line on one set?

Start by confirming that the modem is online, after this, follow these instructions:

If you have a cordless telephone:

• Check that its base is switched on and that the telephone itself is charged
• Keep the phone within the range of the base.

If the issue persists or if you have a non-cordless telephone set:

• Confirm that the telephone wire is connected in TEL 1 on the modem. 
• Call the landline telephone number from a mobile and check if you can hear a ringing tone.
  • If there is a ringing tone, the line is working, and the fault is with the telephone set.  Change your telephone set and check again.
• If there is no ringing tone, remove the wire from TEL 1 on the modem and call again to confirm if there is a ringing tone . If now there is a ringing tone, replace the splitter or adapter you connected with the modem port. After, replace your telephone set and check again.