stopping internal sound

ok, so you load an mp3 into the library. give it an instance name. create a new instance with testSound:mySound = new mySound();
play the sound with testSound.play(); it all works great. but now I want to stop the sound (background music in a game) . I guess letting us do testSound.stop(); would just be too easy....Why can't I stop a sound. I see can stop a sound channel but it only seems to work with external sound loaded with a url?

Thanks