We are at the end of a home remodeling project, and have paid partial amounts along the way. We received our final invoice and it includes change orders that were not at the price given by the contractor. It also includes a 4 month old bill for HVAC subcontractor stating that it is a change order, and that we owe it (plus the contractor's 20%). Our contract states these changes must be agreed in writing by both parties. There is no communication regarding this bill or that it wasn't part of the original contract. I told him we disagreed with these items, and included his e-mails with the original $ amount for the approved change orders. I said we felt the HVAC was not a change order, and was part of original contract. I then said how much I agreed to pay. He replied that he disagrees and full payment is due otherwise no more work will be done (a minimal amount it left). Today, I received a prelim 20 day notice (that he mailed before he sent our final invoice). I'm worried he can file a mechanic's lien even though he seems to be breaching his own contract. I had given him a partial payment of $5000 instead of $9700. After my calculations, I feel I owe him another $1000 or so. I'm not sure what to do next?