Usually Delayed As Having Being Expected

Unfortunately, I am waiting at the airport more than the scheduled, ie, by 6 hours; my flight has been scheduled at 11am at the time of reconfirmation. BUT of Buts, when I check in, the lady in charge just flatly says to me, "Your flight will leave at 18pm".

Why not informing me of the reschedule when the confirmation by the airline office here is done with the phone number, including the place of stay??

Well, and of course, as usual, there is nothing I can do here except simple waiting.