Yeah, just to chime in.
It'd be easiest to think of him as having two surnames here. When he's giving her full name he'll use the von - "Ich heiß' Sascha von Heinz". But if there's a title and surname, the usual way is just using the second part - "Ich heiß' Herr Heinz".
"Herr von Heinz" would only really, in my experience, be used by a solidly upper class person as a signifier of that.
Also, remember to use an article ("der" in your case) - "Ich bin der Heinz Sascha".
Of course, all of that may well be far too much information.