What do you do when a customer falsely claims you promised extra?
Have a lawyer write up a lien document against the customers property. Be sure it includes the cost of the lawyer and the highest allowable interest rate on the amount owed. Ask to sit down with them and review THEIR COPY of the contract. If there is no evidence of the alleged extra work and they see it then you have nothing to worry about. If they threaten to withhold payment then give them a copy of the lien document and excuse yourself from the meeting. Your next stop will be the courthouse to file the lien.