If your Apple Watch no longer responds to touchscreen inputs as expected, then the following steps may help:
If you have not yet done so, then update your iPhone and Apple Watch to the latest software (watchOS 4.1 is not the latest version), starting with your iPhone:
Remove any screen protector, case or bumper that you may have fitted to your Apple Watch.
Clean your Apple Watch, being sure to follow Apple's cleaning instructions:
Restart (normally) your Apple Watch and iPhone, turning both devices off together, then restarting your iPhone first:
If the issue persists, next unpair and re-pair your Apple Watch:
If the issue then still persists, I suggest that you contact Apple Support (mail-in service may be available, if required), make a Genius Bar reservation or visit an Apple Authorised Service Provider again for assistance: