How do I defend against a fraudulent lien?

I recently had a house fire and was referred to a General Contractor from my Public Adjuster,. After months of delaying the project, they finally started working on my house. I found many issues in their work and asked them to pause everything. They ended up quitting the job and overbilled excessively for things they did not do. They did not finish the job and they failed the electric and structural inspection from the city. They are asking for the entire amount, despite them not finishing the job. I have evidence from an independent inspector showing that they overbilled by 100% or more in many areas inside the scope of work. After sharing the discrepancies with them and trying to resolve the situation, they came back threatening me with a mechanics lien and saying that they will be holding my personal belongings and not giving them back until they are paid. (They have some of my contents in their warehouse because of my fire). They have been unprofessional, condescending, and quick to threaten rather than try to come and fix all of their issues. On top of that, I don't think they had ever given me a contract to sign. How do I deal with a GC who is committing blatant fraud, coercion, and strong-arm tactics to try to get paid money that is not owed to them? Especially if there is no contract in place. Thanks