That's very good news: Amex are very much aware of BA's IT issues and I would hope that ultimately they will be helpful in making sure the money is recovered unless BA can completely prove that you made the cancellation after booking. Typically Amex does not get good information from BAH about their bookings, so again that works in your favour. However to repeat, this is the very last step, when BAH confirms that there is nothing more they can do.