My iphone was stolen!

If your phone is switched off, or does not have a connection to the Internet, it may be unable to report its location. I assume that since you say your watch "stopped tracking" your stolen phone, your phone had Find My enabled, and your watch was tracking your phone for a while.

See the Related Article: If Find My is offline or not working - Apple Support

Also: If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

I hope that you have already carried out step #2, marking your iPhone as Lost. That would trigger Activation Lock, an anti-theft mechanism designed to make your phone worthless to the thieves.

Note that if you carried out step #7 (removing your stolen iPhone from your list of trusted devices), that would clear any Activation Lock, allowing the thieves to reset your phone and "make it their own." So you might not want to do that.

Also, beware of phone calls, messages, etc. from people claiming to be with Apple Support and supposedly wanting to reunite you with your stolen phone. They are not with Apple Support. What they are after is to get you to provide information or take actions that will let them make YOUR phone "their own" and that perhaps will let them scam you in other ways.