Poor VOIP Service

I am increasingly getting frustrated by the continuous lack of a reliable phone service at my parents property.

Since changing to digital, the phone regularly either fails to work, or cuts during conversation.  My elderly parents who are not in good health.  Yes they've called an engineer a couple of times who have come and gone and still the service is poor. BTW I was angered when they told me you would charge for a call out if there wasn't a problem with their line. 

I am increasingly worried if something happens to them and they cannot get hold of the family or emergency services, especially as my mum is alone most of the time.

Please can you contact me and find a solution to the terrible service that they are receiving.