OS: Please advise me what is the best way in this situation?
While I understand the importance (to your builder) of a fixed delivery date, what you seem to have is worse than a late door, you have got no door.
This is not legal advice, it's practical advice. Go back to the door manufacturer and attempt to renegotiate the door order - if you really want a door.
If you no longer want a door at all, that is something else. You should have looked at the order T&Cs before you took unilateral action.