I believe you're running into another version of the same problem I describe here:
https://www.construct.net/en/forum/construct-3/scripting-51/declaring-objects-script-160208
To put it simply, each script block has its own namespace, so the 'MyStreaming' variable isn't exactly destroyed - it simply cannot be accessed outside the block where it was created.
The solution is to declare your stream in a way that's globally accessible. I don't know much javascript, so the way I've started to do it is by creating things by the window object, which is probably a dumb way to go about it, but works for me.
What you'd do in your example is instead of declaring your stream using 'var myStreaming =', declare it like 'window.myStreaming =' - the window object will be accessible from your other block, and thus 'window.myStreaming.stop()' should hopefully work. Good luck!
Thanks, it is true that windows works to keep variables from one block to another, but there is something that my code is missing, an id to identify the audio that has been played, since I can not even stop the audio within the same block.
I have to investigate how to identify that audio, although I do not know javascript I will not give up!