If I were them, I'd send the tech guys out, claiming to fixed the line. Put you on some awesome line priority over all other lines, no more problems for you. And you stop complaining.
Until your neighbour does.
If they consider the possible repercussion to this is too great, they might tell you that there's nothing wrong with your line. And that you may need different equipment. In the mean while, give you a better line some time later.
The point is, when you use their service, they can shaft you anyway they want. They don't want to shaft you if they can, but they have to. Numbers are looking pretty ugly for them.