Just thought I'd follow up here for all those still having difficulty.
It's possible someone here could have a genuine faulty Apple Watch (maybe a faulty Modem?), but for the vast majority they don't and this is an o2 issue pure and simple.
After weeks of suffering, I left O2 last week and in my case joined Three (but the other big networks work also) and since joining Three, my watch has been perfect. This is the same watch which got the no connection on o2 after 10 minutes.
Not only that, but even though I was in a 3G/4G/5G area for o2, my watch was never connecting beyond 3G. I got use to Siri being slow and whatnot and just thought that's the Watch's low power modem or similar and I accepted it as normal.
I didn't know any better, until I joined Three and noticed that the Cellular Logo on your watch changes to '4G' when on LTE and it never did that while I was on O2 across multiple watch generations even though I was in a 4G/LTE area with strong signal.
I know the watches don't have 5G, but it makes me wonder if o2 4G doesn't work with the watches either, or maybe the masts around me use 4G on a frequency that is unsupported by the Apple Watch. Be curious to know if others ever got 4G on their watch with o2 when it works or if its only 3G service.
Either way, the fundamentals of using the watch on the go completely change when its on a fast, responsive 4G network compared to 3G. Siri is instant, Apple Music streaming is instant. It's game changing while on my daily runs if I'm honest.
So all I'd say is keep at it if you can, this isn't an issue with your watch, keep pestering O2 until it's fixed and keep demanding a refund of the charges until it is. And if you don't want to wait, jump ship.
The other networks work with both the Ultra and Series 8.
Last time I'll be posting here, but wish everyone luck and hopefully you get it sorted one way or another!
