To be honest, relying on "passive" communication for an exceptional issue that requires pro-active behaviour is probably going to get you nowhere. This is the kind of task where you really probably need to speak to a real live agent and try to convince them to "go beyond" in order to help you.

That said, the simple fact of persuading Garuda to undo the transaction may just leave with you without any miles. The "systems" will still probably see that the miles were already claimed and refuse to grant them in the other program. As such, you would have to get Alaska to "go beyond" too.

So this will probably serve only as a learning experience for the future. Never casually associate an FFP number with a booking.

Another tip: As this topic has nothing to do with Flying Blue, and only tangentially has anything to do with Air France, the Alaska forum would have been the natural home for this query.

By the way, contacting Air France about this issue is a complete waste of your, and their, time. Air France operated the flight and your issue is not with the flight. At best, for the tangential issue of FFP mileage, Air France would fob you off to Flying Blue - but this has nothing to do with Flying Blue either. As such, they were correct to send you to GarudaMiles. Your issue can only be resolved by starting with GarudaMiles. Air France has no way of making Garuda do anything, nor any requirement to do so. And until you get Garuda to uncredit the miles - which is a big ask - then there is nothing Alaska can do, either.