I hired a company to clean my house after a puff back, They didn't do half of what they were charging me for. The owner agreed that the job was done poorly and had to be redone completely. I told him I would pay him for what he did do and hire someone else to to the rest. We filed a lien for the entire amount. He is all so trying to charge the insurance company for work not done.
If the lien is valid on its face (and based on your defense I'm assuming it's not because the lien itself it out of order), then you would have to await the foreclosure action to challenge the underlying claim. If you want to have that fight sooner rather than later, you can serve a demand to foreclose the lien. If the contractor starts the foreclosure action, you can have that fight now, rather than wait. However, the contractor may not file the lawsuit (many times the lien is filed as a collection effort), and then the lien would be subject to being discharged.