I would think that you definitely want this to be an email contact so that you can provide PDF copies of the relevant documents, including the receipt and your CC statement showing the charge posting.

Your mention of the forex fee suggests to me that the agent at HKG quite naturally posted the charge in HKD and that when AA went looking for US$350.00, there is no such collection under your PNR. Rather, there is a collection somewhere for approx HKD 2,715 and the corporate security folks have not drawn the connection.

Thus, a prominent mention of the fact that you had a forex fee imposed by your CC issuer, ordinarily irrelevant to AA, and that you may have been charged in HKD and thus the $350.00 may be off, may be worth mentioning.