I had to google chorus to find out who or what they / it is. It would seem to me that you need to try another ISP. Everything you have tried points to it being their problem, either at the server, or in the equipment which supplies your service. Sorry, no other real solution suggests; you've tried all of the things I would have in this unsatisfactory situation.
Last edited by FullOppositeRudder; 3rd Dec 2019 at 21:37.
Reason: Spelling