Dude needs some self-awareness. It appears ignoring him was exactly the way to get his attention, since he can't think of anything else. Although her father intervening and disposing of his letters is also very dumb. He should either tell him to desist and that his letters won't reach her, or let her decide wether to answer or not. Also, they must have been in an official relationship, so has the father confirmed that their engagement is over? If she just tells him they're done, and this is not acknowledged by annuling their engagement, it's natural that he would think she's just playing games.