So you have to make a complaint with NowTV, once your complaint has been open with NowTV for 8 weeks, they will automatically send a deadlock letter (although cheekily the email doesn't state its a deadlock letter, just if you want to complain further (here is the process)).
Then you file a complaint with the CISAS, who are the ombudsman for NowTV.
I think you need the deadlock letter, otherwise the ombudsman doesn't entertain.
Try and keep all transcripts of chats with support and emails you send them as evidence too.
It's insane that this problem is still unresolved but just to add to potential workarounds for this problem I found that for me, unblocking the URL pubads.g.doubleclick.net from my Pi Hole (network ad blocker) resolves the issue. Not ideal as then I get loads of ads on all other devices on the network so I unblock it, start Now TV, then re-block it.
You recent update appears to have broken the workaround.
The "Sorry, NOWTV in unavailable" screen now has a retry button that wasn't there before, but now pressing "back" does not bring up the list of apps.
Software update 18.104.22.16801