I fully appreciate your frustration. Someone from the Plusnet Help Team ought to be able to look at you connection and see if any of the VLANs are congested. Clearly something is. I don't know who on the team is looking at these sort of issues these days, feedback seems pretty poor I'm afraid.
Hopefully one of @Chris @MatthewWheeler @HarryB or @MattyC will take a look and add some comment to your ticket. If you post the ticket number that will probably help them.
