When I let my anger take control over the lying and slander I see then the other guy wins. "No one can insult you without your permission". Instead of anger channel those emotions into resolve. What you are experiencing is literary terrorism. Its intent is only to disrupt for it has nothing else to offer. I will not say my method is easy but I have learned that it infuriates someone who is trying to anger you when you either ignore them or respond calmly.
Years ago a comedian, Brother Dave Gardner, unknowingly gave me some advice in one of his comedy albums. "Love thine enemies and drive em nuts. You owe it to your friends".