Defect front door - who is my contract with?

the_lunatic_is_in_my_head

Sounds like you can reject OP but you can also seek a price reduction, question is would some money back resolve the matter for you? If not push for a refund and buy a new door. Company is on the hook for the costs involved. 

That said holding fire for a short while to see if the manufacturer will agree a new door at no cost to you might be pragmatic. 

TELLIT01

The door and frame seem to have been provided as a single purchase to whether the issue is with the actual door or the frame is really academic.  There is a fault with the purchased product which needs to be sorted out.