Ok scenario time. You work for a dude because you need a job badly. It turns out to be a scam. YOu leave and blow the whistle. Then you start your own legit company and do well while impressing a lot of customers. Then, dude finds out your company name and slanders you all over the web, including ripoffreport.com with nothing but lies (some outright disgusting), all in retaliation. How do you deal with it? Do you ignore it? Do you take it to court? Change your name?
That is slander and/or libel (not sure which), which is illegal in most countries, so contact him and "remind" him of that.
I would get a lawyer. When a lawyer calls him he would probally get more scared then when you call him yourself.
Take it to court. Or just call the dude first and explain to him that you will get him to court unless he stops doing that.
Definitely contact a lawyer and see what you could legally do. Also, don't call this liar, contact him only through email so you have some tangible record.