[Ratitong]

I recently bought a round trip ticket LA-SD-LA online at American Airline website for my 17 year old son. It is a no-cancellation or no refund tickets. Any changes after purchase might incurr cost. That's what I understood. We called to find out how much we have to pay because of a change of schedule. The additional cost is very high so he took a train instead for the LA-SD leg without teling American Airline (i.e no show). On his return trip, when he was at the SD counter a few hours before the flight time, he was told his ticket was automatically cancelled. He again was forced to take the train to catch up with his international flight. My question is, is it a rule that American Airline reserved the right to cancel the ticket if he didn't use the first leg? I tried to search such rule but can't find it any where. Does anyone has this experience before? I tried to contact AA customer service but unable to talk to any human. Can anyone give me any suggrstion? Thanks.