No ringtone, phone not ringing, fully charged phone says 'check phone line'

Hi,

My 89yo father has a cordless phone setup with the main handset plugged into the back of his hub. The phone currently has no ringtone and does not ring even when appearing to ring from the caller's perspective. It just says 'check phone line'. I do not live nearby but have managed with help from others to factory reset the hub, unplug/power and re-plug/power the phones without a positive outcome. Everything has currently has power, the hub shows a solid white bar and the phone is fully charged. I'm not sure what next step I can take to resolve this. Any ideas?