Unfortunately in North America your not entitled to denied boarding compensation unless the flight was oversold. You might be able to recover damages by suing them in small claims court. The fact that they admitted their mistake plays on your side. This is why we need EU style laws in North America to punish airlines who engage in illegal behavior. You had a contract and they chose not to honor it. I would ask for any forfeited prepaid expenses as well as an amount to the price of buying points on American Airlines. Good luck!