Thank you for using JustAnswer.
I'm sorry to hear about your situation. That's pretty extreme. There would not be a case for "defamation" (because a true statement, even if damaging, cannot be defamatory... only a false statement of material fact can be the grounds for defamation). There could be a case for harassment, if you could establish that the behavior was objectively harassing. But that has its own problems. First of all, you need to show that no reasonable person could think that this is "okay" behavior. Rather, everyone on the jury would have to determine that it is per se harassing. And while I am with you here in that I think that it's harassing, I'm not willing to necessarily bet that a jury would agree. But more importantly is that with any lawsuit you have the burden of establishing "damages". That is, you have to prove the specific dollar figure that you were harmed as a result of the harassment. For example, if the landlord cancels your lease and you have to get a new lease for a higher amount, and the only reason that the lease was cancelled was this harassment, you could have a case (again, after proving that the harassment was objectively unreasonable). But you can only go after the actual damages that you can establish, and as it's a "tort", you wouldn't have a case for attorneys fees and costs, so it would be a case that might cost more than you would ever recover.
So in short, if you don't have any proveable economic damages from the customer's behavior, it would still be without recourse civilly. Now you could tell the customer to stop harassing you by contacting other third parties, and if it continues, you can contact the police. Criminal harassment is a different matter, and that's something that they might pursue. But it doesn't look like you would have a civil case against the customer, even though I agree that the behavior was awful.
I know this is probably not what you wanted to hear, but it is the law. I hope that clears things up anyway. If you have any other questions, please let me know. If not, and you have not yet, please rate my answer AND press the "submit" button, if applicable. Please note that I don't get any credit for the time and effort that I spent on this answer unless and until you rate it positively (good or better). Thank you, ***** ***** luck to you!