I looked through the code, and I see a few things wrong but I'm not sure if that is your problem.
First, the Global script is running every frame (on process) when you should just call that function on level changes or on some event (when the difficulty increases), and not every frame.
Also, these are not the same thing:
print(Global.enemylvl)
print(units)
The first line should get the actual global variable, the second line gets a copy (whenever you initialized the variable) and it will never update. If you are working with global variables, you always need to access them through the class name (Global in your case) otherwise you will be assigning a new value to a copy, which isn't what you want.
Otherwise, I'm not sure. Can you post a small section of the code here that you think isn't working, or let me know what the print statements say? Also, maybe just zip up the whole project folder and upload it somewhere (like Google Drive) so I can test and take a look.