When I got my repair back that was a half-*ss job like yours, I pointed out that literally half of what was quoted was missing, and they immediately told me that they will send it back to the atelier as a priority pack, to get is redone as quickly as possible, free of charge of course. That should have been the case with you too I believe. If they mess up the quote, that is their problem. They gave a written offer, changing that afterwards is not only not nice in the luxury world, but in most places it is straight up illegal.