https://criminal.findlaw.com/criminal-charges/extortion.html
"Most states define extortion as the gaining of property or money by almost any kind of force or threat of violence, property damage, harm to reputation, or unfavorable government action."
My IANAL interpretation of that would be extortion wouldn't apply here. Because my security deposit is legally mine, and they were holding it on my behalf, I'm not gaining anything. Demanding my own property back is not the same as profiting. If I had demanded my deposit back plus $1, then it would be extortion. Maybe. Again, IANAL. Fortunately the statute of limitations makes me safe, as this was long ago :)
> "Most states define extortion as the gaining of property or money by almost any kind of force or threat of violence, property damage, harm to reputation, or unfavorable government action."
Under your interpretation, if Alice took Bob's lawn mower without permission and refused to return it, and Bob told her he would call the police and report this unless she returned it, that would be extortion. The police coming and arresting Alice for theft is an unfavorable government action from Alice's viewpoint.
Similarly, if you were contemplating suing someone for damages over a harm you felt they did to you, it would be extortion if you told them you were going to sue to so unless they agreed to settle.
The son was likely guilty of some sort of larceny (theft by deception) and it may have been a federal offense, especially if it crossed state lines or involved the postal system.
Collection agencies (or whatever they are called in the US) hound people for money they owe to third parties. They often call your workplace or relatives as a way to get you pay.