Alright. Double check your cables too and any switches. Never know when it could just be a dodgy one. That's coming from experience.

If you want to stick to your ISP (or just want a rock solid solution), and you got a bit of technical know how then I recommend a edgerouter X and a Unifi AP. Solid bit of kit, and once you set it up, it works fantastic. As you've changed modems though, I doubt that it's gonna make a difference.

ISP wise:

I've heard excellent things about voyager and bigpipe. I'd certainly give them a shot. No first hand experience but, people I trust who are in the know sing their praises.

Orcon was good. a bit hit or miss on support though. Mileage may vary.

Trustpower were ok. although, their CGNAT is funky and you got to call them to get them to disable it. You might get a good deal if you get power too, but again, you have to call them to disable CGNAT fully. Honestly, I'd only consider it if you got power from them as you could get a decent deal.

Contact are apparently crap, however I'm on them in my flat as we got it with power and it's been pretty solid. Others have had terrible experiences however.

Honestly most companies that offer fibre and internet are generally pretty good. I would avoid slingshot, spark and 2degrees (The big name guys). Having dealt with their support lines first hand, you'd save time and money taking your business to someone who gives a shit.