Most unpleasant Travel

Me and my wife plus my 2 infants was suppose to travel on 24 Feb 2015 on flight 3K 513. We arrive and check in 2 hours early and got our boarding pass and proceed to the boarding gate waiting to board the flight. We waited there and then i received a call from Jetstar staff asking me where i am? I told her Gate C 16. And ask me why was i doing there when the gate was at D 48. Then how come my boarding pass was stated C16. So we miss the flight and Jetstar was cool enough to move me and my family to the next available flight. Finally arrive at Bangkok but without the baggage which contains all my children milk powder, clothes and gifts for my relatives in Thailand. Till now i still not yet get any response from Jetstar regarding my baggage. How could this happen and it really causes me a hell lot of trouble.