Your iPhone must be within normal Bluetooth range (about 33 feet or 10 meters) of your Apple Watch to unlock it. If Bluetooth is off on Apple Watch, enter the passcode on Apple Watch to unlock it. Are you sure you are entering the correct passcode for the watch? (It may be different from the passcode on your iPhone, depending on how you initially set it up. See:
Lock or unlock Apple Watch - Apple Support
If neither of those are the problem the use the "Contact Support"link at the top-right corner of his page. Also, the first (and simplest) thing to try if something isn’t working right is to restart your Apple Watch and its paired iPhone. If necessary (device not responding), try a forced restart. Both methods can be found here:
How to restart your Apple Watch - Apple Support
Restart your iPhone - Apple Support
If that doesn't help, the next steps would be to unpair and pair your watch again and restore from the backup. This deletes all temp and corrupted files and re-indexes the file system.
Unpair and erase your Apple Watch - Apple Support
Set up your Apple Watch - Apple Support