Bond around the lien and tell him you will see him in court. Take a million pictures and probably some video, document every conversation you have with him and hire a junkyard dog for an attorney, you can win this but you must be diligent.
I was a contractor for over 20 years and we did all of our own cocrete work just to avoid these types of problems. Concrete work is a low margin, easy business to enter (doesn't take much money to get in it) and for these reasons and several others most concrete contractors don't have the...