Line Cord Error, Any Ideas?

[HavencroftKev]

I've noticed for a few weeks my landline has said "Line Cord Error", I had forgotten about it as I seldom use my landline. However today the phone rang but I couldn't answer it and the handset was still displaying "Line Cord Error". Does anyone have any ideas?

[Mark39]

 @HavencroftKev do you have Internet calls? Or standard calls?

[HavencroftKev]

My phone is plugged into my router, so I'm guessing internet calls. I used to work fine.