I hired a contractor to install a specific brand of a high end tankless hot water heater. We agreed on the price for material and labour and the contractor started the work. After the install was done, I noticed that the contractor installed a cheaper version that cost less than the originally agreed water heater. I have refused to pay for any work until the work is corrected but the contractor has threatened to file a lien if I don't pay in 30 days. What are my options in Pennsylvania if the lien is filed?