networksetup -disconnectpppoeservice not working
I am going here on a hunch !

sudo networksetup -disconnectpppoeservice HUAWEIMobile-

sudo networksetup -showpppoestatus HUAWEIMobile- 


You confirmed it says 


  connected


I further assume when you activate the PPoE service it will respond with user + password request.

Since that information was not supplied it will wait for it and refuse your disconnect request.

So we can try the activate with user name and password, then do the disconnect, you can find the appropriate command set here.