Hi, WebbyFromUK!
I have had many issues before with my Apple Watch and iPhone, and I consistently have tried resetting/unpairing my Apple Watch to start over. This being said, I have found that 9 times out of 10, the issue resides with the iPhone and not the Watch. Try deleting and reinstalling the Watch app, if that does not work, try using a computer to create a backup of your iPhone. Once you have done that, Factory reset your iPhone, but do not restore the backup. When setting it up, do not use an Apple ID. Once set up, try setting up your watch. If it works perfectly fine, reset your iPhone and erase your Apple Watch. Restore your iPhone from the backup, and try everything again. If everything runs smoothly afterwards, then everything is fine. If you once again have the issue after this process, then my only suggestion is to store important information (Keychain, Contacts, Messages, Etc) in iCloud. Factory Reset your iPhone, and do not restore from a backup. Instead, set up as a new iPhone, but use your Apple ID and iCloud to sign in. Your Keychain, Contacts, etc. should slowly start showing up. Set up the Apple Watch. If it works, then reinstall your apps and you're done.
This is a frustrating and tedious process, especially when it contains resetting your iPhone, but when you spend blank on a watch, I get that many people including myself would do almost anything to get it working.
