[QUOTE=Klostersgirl;746314] My husband says its just some bünzli Swiss family trying to make a fast buck and he'll deal with it when they call and my son says the boys just a "cheeky idiot" trying to make a fast buck!
QUOTE]
Sounds about right to me - let your husband deal with it.
While Swiss kids may be independent - a 13 year old boy is still a 13 year old boy in the sense that he has neither the developmental readiness in this type of a situation to deal with an adult - in terms of finesse and tact - hence his crack about you being a nice mother.
If his mother's intention was to teach him to take responsibility and make the phone call himself, that was fine for the first phone call.
As you tried to engage on an adult level with the note, it should be clear to his parents that you've opened the lines of communication to them. If they don't respond that's their problem. If the son would call again, just tell him nicely that you prefer to speak to one of his parents.
You don't know what type of a home he comes from and what kind of pressure the mother may be putting on him. He is after all only a kid.
I hope for your sake they just let it go. Don't worry the "punching and pulling" stage ends around 14/15 years old