You need to tell python your zombiepos is an array before you assign to it through indexing:
zombiepos = []
for _ in range(10):
zombiepos.append([-1,-1])
you'll have to change the for statement in the while to range(10) as well.
the global statement is unnecessary. you'd need to use it if you were accessing zombieamounts in a function.
also, as mentioned in some of the comments to your code, when you access the items within zombiepos you need to use square brackets [] not parentheses