Drywall contractor question/complaint

[Traci Lovelace]

The drywall contractor we picked has been a fiasco of drama, over runs and excuses after excuses.  They were supposed to be done on the 12th, which was an extension to begin with. 

Now, they are asking for $1000 more than the original invoice and a draw today. The original quote was $6800. The contract says pay materials up front, rest at end. They are running so late I have moved my floor guy twice And they are about to run up against my painter. I have remained polite, but the additional bill for things I feel they should have seen up front is really the last straw.  Looking for advice. Thanks-