Crooked contractors

[u/fargo-temp-account]

I am in North Dakota and I recently had some remodeling work done in my house. During the installation, some of the fixtures were damaged. The project has taken way longer than it should have and it just want it to be over with, so I asked the contractor for a $500 credit for the damages. They are refusing and threatening to start collections and lien proceedings if I do not pay the final invoice (which was $5k higher than quoted). My position is that the project is not complete until these damages are either repaired or credited. Am I screwed?