I had a second HVAC system installed in my home. I already had the equipment but it was too large for the space so my HVAC contractor said he would swap for a smaller unit and give me credit toward the work to be done. The job was started but took over a year to complete. There were several installation issues that needed to be fixed with 4 additional visits. I have since received a $1200 invoice with incorrect date. Being that it took over a year to complete this job, I requested a detailed invoice to include dates of service, an outline of how the credit was applied and of the work performed. I also requested that they take into account the time it took to complete this job when revising this invoice. The contractor has refused to provide me a revised invoice and is now threatening to put a lien on my home.