At this point I too would be a lot more worried about the second-order problems from American Express if they believe you are somehow involved in a fraudulent refund scheme. I'd escalate to the executive office - email the CEO and there's a group that tends to respond - proactively and send them copies of your correspondence to date with AA attempting to rectify the issue. If you can get someone to note your Amex account ahead of time that this is just a comically large error and not the beginnings of some type of money laundering or other financial crime web, you may save yourself some heartache. This is especially true once American Express, either through your prodding or their own automated processes, decide to send you a credit balance refund -- one can only imagine the shenanigans a six-figure account balance refund check from a single transaction not associated in any real way with an actual charge will set off on their end. They may even hold on to the money in a frozen account and then, with that type of luck, AA will come knocking with a legal letter looking for their $100k which of course is stuck frozen somewhere inside the belly of Amex. Best to try your damndest to document now.

As for AA, the hell with them.