then you seem to do something wrong since i had no problem beating it. keeping only 2 to 3 units attacking with only 3 units attacking everywhere. i made the game into multiplayer and maybe you see how you should play it. and you should analyze everyturn and you will notice that i just placed everywhere like 2 or 3 units and did transfer moves befor attacking moves etc...
https://www.warzone.com/MultiPlayer?GameID=15485045