I hired a contractor to do work on a renovation. We agreed upon a price and I made all payments in full accordingly. 6 weeks after starting the job, he claims he underbid the job. After making final agreed upon payment, he handed me a bill for "extras" that is 2x the amount of the original agreed upon price. At no time during the job did he ever indicate which work performed was extra and how much the extras were going to cost, or receive approval to proceed. He is now threatening a mechanics lien. Is his lein valid?