Consumer Redressal

My son Ammar Z C was travelling from bangalore to pune on Indigo flight 6E 408 on 9th March 2015 at 5.35 am. We had checked in the prior night and collected the boarding passes at 4.50 am from the indigo counter. At 5.10 am I get to know that the flight has left and my son is sent back from the gate saying he was late for the flight. He had to purchase fresh tickets and fly to pune on the 3.00 pm flight where he missed his exams and day at school. Where can I file a complaint for this . Pls help. I think they have conveniently off loaded some passengers due to excessive bookings. Pls help. Also 2 days later my husband flew the same flight to pune and a passenger boarded the air craft at 5.35 am after which the flight took off. So why this trouble for such young passengers? Is it because they are novices and they can be trampled upon under twisted laws?