You can freeze soup when it has milk in it however when you do freeze the soup with milk the milk will separate from the soup and base but you can add some more milk or cream and whisk it again to make it just as fresh as before.
It's best to just refrigerate the soup that has milk in it and then eat it within a few days but no harm will be done to the soup and milk if you do freeze it except for it separating and not being as fresh tasting as before.