American Airlines Customer Service Misinformation Internet

On May 7, 2013, a ticket was issued through Vayama.com. I had 48 hours to cancel at no additional cost. To arrange my seating, they told me to call American Airlines. When i contacted them, American Airlines told me everything was all set. I noticed that online 2 seats weren't assigned yet. I called back. I eventually paid $25 for American Airlines to seat me properly. They told me that they had printed out the actual tickets, and could see that I was all set. When I checked again, a few weeks later, I noticed that i was on 2 flights for the same route on the same day. I wanted to be on QF 576 (Which I was told I was on, and seated on) but it also showed flight 580. American Airlines admitted that they had made a mistake. They told me that I was never actually on flight 576. An agent put me on flight 576, but in reality I was on flight 580. This was a shock to me, since this entire time, everyone told me I was all set on all my flights. Included in the flights listed was flight 576. Because of their mistake, I am now coming in to my destination much later than I had anticipated. I am missing the entire day. Had they have told me on May 7 that I was on flight 580, I would have been able to cancel my trip and reschedule at no additional cost. Now, Vayama is charging me $605.00 (as of June 5) to change flights. Even though American Airlines admits that they gave me misinformation for over a month, they still refuse to compensate me.