Wow. Great reason to cross Focal off your list. Too bad your dealer did not tell you that ahead of time. Almost sounds like a no win. Blow the bucks to fix them just to have them break again. Fix and sell them--I’d have a hard time doing that with a known quality issue. Sorry to hear your misfortune but your post is valuable to others looking to purchase headphones.
P.S. I'd find a new dealer as well
P.S. I'd find a new dealer as well