I am a contractor. We completed the job for a customer with a remaining balance of $7000. There was a damage to their microwave. We agreed to reduce the balance by $800 for a final balance of $6200. They have not paid that and they don't return my calls, email or text. Job was completed Feb 3rd, we reached an agreement on March 14th
Hopefully this was all documented in writing. If the customer isn't responding to you, then sometimes sending a letter with a law firm's letterhead gets them moving. To file a lien, you'll want to make sure you're following any notice requirements before filing a Petition to Establish (and Enforce) a Mechanic's Lien in the Circuit Court of the county the property is located in. It's tough to give specifics without knowing more about your scenario, but generally, this is the path you want to take.