If you can't call for help, try to get the attention of the people outside the elevator. If you've tried the call button or tried calling for help and have gotten no answer, then your next bet can be to try to shout or call for help. You can try to bang on the door of the elevator with shoes or other objects and yell to alert passersby. Depending on the sound transmittance of the door, tapping firmly with a key on the door may make a loud sound throughout the elevator shaft. Shouting can help alert people who are outside the elevator to your situation, but you should know that shouting or yelling excessively can also cause you to panic more, so make sure you try to stay reasonably calm when you are calling for help. pry open the doors and walk out. Look around the elevator to see if you can find any objects on the walls that can help you pry the doors open.
Search the roof of the elevator for the service hatch. Attempt to force it open and crawl out. Even if you do get out through the hatch, there still may be no way out of the elevator shaft. But if you find yourself in a real emergency, then this may be your only chance.