Why won’t my stand alone watch connect to Wi-Fi?

I wasn't aware that Watch supported Wi-Fi Calling. It would certainly be controlled by your cellular provider if it did.

If you are having trouble connecting to Wi-Fi itself then consult this article

Connect your Apple Watch to Wi-Fi - Apple Support

I cannot get my Watch to do anything at all in Wi-Fi unless the iphone is nearby. I have reported it at

https://apple.com/feedback

Unless someone else knows why this doesn't work...

Use Apple Watch without its paired iPhone – Apple Support (UK)