Versatis landline phone, screen displays impossible

Good evening,

Earlier I wanted to call someone using the landline, I dialed the number and it said impossible on the screen. I tried calling the landline from my mobile, usually the number is displayed on the screen but this time it just showed call and when I picked up, the call ended.

The landline phone is a Versatis F230 Voice.

If anyone has had this issue before, could you please let me know how you resolved it?

Thank you in advance.