One of the worst things to do is not to be nice to a bad client - saying something that isn’t nice to your client, no matter how rude they are, is usually a lack of professionalism from the seller’s side. I’ve talked about this with CS before, and they were very clear that a seller must be polite and professional at all times even when the buyer isn’t nice at all (you have to learn to control your anger and direct it somewhere else - go chop some wood or something to get the anger out).
If Fiverr changed his rating to 1 star, you just lost all leverage of changing it back because you didn’t behave politely and you weren’t nice to your buyer If you would have kept your cool, you would have had an advantage and Fiverr may have quickly fixed the problem…
So you said something not nice to them - did that make you feel good? I bet it did, but just for a moment, because from what I see now you feel worse.
Why am I telling you all these? Because I’ve been in your shoes, I’ve done the same in the past, and I’ve learned my lesson. Now, whenever I see a buyer behaving badly, guess what I do? I am glad because I now have leverage over the client, and I can ask CS to do or change things just because of how that buyer behaved or treated me. And I talk politely to the buyer, and if I really need to threaten the buyer I will do so by using a formal legal-like language and make references to the Terms of Service and how they broke the rules.
P.S. read the Terms of Service page, learn it & make it your friend, you can’t imagine how much power it gives to a seller in such scenarios