I've live chatted with Zen twice today. This morning not so informative, this afternoon was much better.
Basically they're trying to find the common cause but it's proving difficult because it's not a common gateway/exchange affected and it's only some customers not all.
They can't give a timeframe for fixing.
They don't want to put a service/status update on the website because it's not a particular region affected. Personally, it sounds like they're playing for time, as soon as a status update goes on to the effect of reduced throughput and packetloss they'll be inundated with calls. Not what I expected tbh, but I'll judge them on how many bad evening's internet I get and seek recompense accordingly if it lasts much longer. Already 7 days into it.....