WiFi not working again

we are having problems with our wifi again. To date in the year we have been virgin we have had three or four replacement routers which each time causes hours of work, not only trying to re pair the three wifi pods but also re connecting all of our devices as we have most devices connected by the internet. 
Every few months the WiFi begins to drop out and we get the following message:

I then spend ages on the phone trying to explain the problem and they end up sending an engineer who changes the router and leaves and we start the whole process again. 
We have apparently had a new line put in to our property but that hasn’t helped. 
I can’t believe that your routers are all faulty, should they not last longer than a few months. 
Is there a way to fix to this issue without changing the router again? I am sick of paying for a service that doesn’t work.