OP handled it how I would have. I usually only fly in the back for short flights, so I dont put my seat back more than half way. I was flying with my father in law and the kid in front of him slammed his seat back and my FIL grabbed the seat and forced it back up. The kid(10ish) didnt try again the rest of the flight. Pretty sure that is the wrong way to ask someone not to put their seat back!