What to do if Apple Watch Series 10 sleep data is inaccurate?

I’ve spent several hours speaking to Apple Support but no further forward. All settings checked and confirmed. It records I’m in a sleep state by showing light blue bars and an average number. However it’s only ever recorded additional data such as core and deep twice. Both times after a complete re-install of watch and phone. Every time I contact support they go through the exact same steps and then say they will call back in 1 or 2 weeks when data has a chance to collect. This is rubbish as data collected on very first night I reset it. It feels like they are just waiting to warranty to run out. They refuse to replace the watch. I would be happy for them to supply another watch which I would pay for and if it worked I would receive a refund and send them the non working watch. If it didn’t work then would assume it must be phone related. This is not the Apple service I expect.

[Re-Titled by Moderator]