Hi wasimp and welcome.
I'm really sorry you're having connection problems. I know how annoying that can be. It really shouldn't take 3 replacement hubs, engineer visits and resets to get to the bottom of this. I'm sure I can help. Can you try a quiet line test by connecting the phone directly to the test socket and dialling 17070 option 2? The line should be clear of noise but if you hear any popping or crackling it would point to the problem being with the line as opposed to the broadband connection. Once you've done that drop me an email with your details and I'll look into the problem for you. You'll get the contact the moderators link in my profile.