How to make someone unfly with commands?

Hello I am trying to make commands so you can fly and unfly in Survival Mode. The fly command works perfectly but you don't take fall damage for some reason, is there a way to fix that? Also when I put in the unfly command to remove the fly ability you still can fly in survival how can I fix that?

Note That I don't know how to add images to a post so I had to use imgur, sorry. 
https://imgur.com/gallery/pfgjqPB