In short, don't give them attention.
Trolls just want horrified reactions, so typing long comments about how horrible they're being is exactly what they want. It's better if you just don't give them the satisfaction. Just call an admin, report the post, and unfollow. That's it. If you don't freak out, they don't get the satisfaction of a reaction.
Plus, it's a lot less strain on your brain if you don't try to reason with people who just want to cause anger.
