No, you aren't being harsh at all. I'd be SO mad too! This reminded me of the time when my boyfriend and I were 16, and he spent the whole summer visiting his grandparents. He would call me everyday, and we'd talk for HOURS ... he easily went over the minutes in his plan. When the phone bill came back, it was ABOUT $1000. His parents went through the roof and made him get an after school job. He's given his parents back that amount though, plus more, 6 years later. Took awhile, but it's paid
Have you thought of getting him a pre-paid phone instead? That way, he'll have a phone in case of emergencies, and there's no way he'll go over minutes/usage.