Look at it from my way, you find out what looks like you student breaking his word behind your back, you confront him about it, and he only acts annoyed. He won't tell you how it's not true, just that it isn't, and even when he's saying he feels regret about something, he still looks cross at best, and unwilling to change at worse. I told you that I want to believe you, but if you were in my spot, would you?