Re: Online chat
Plusnet closed Chat a month or more ago although, confusingly, some links to it still exist on the website. If any of these do work they only take you to a bot and deal with sales.
The ways to contact Plusnet Customer Support are phone (as you say usually busy), or a post on these forums or Facebook / Twitter. A staff member should pick up your post here but it may take some time during this crisis. A bit more info might ensure it is picked up by a staffer with the correct skills.