Anyone who offers to retrieve hacked or stolen coins is a scammer themselves, there's simply no way to do so unless you can somehow get the private key of a scammer, which is nearly impossible. Even a good private investigator won't be able to do anything most of the time, especially since the scammers can be anywhere in the world. A tiny chance to see your coins again exists if the scammers get caught be law enforcement and the coins are retrieved by them.