GC filed a lien AFTER he gave me an unconditional lien release

[M P.]

Hello.  We have a Texas commercial contract where the GC made numerous breaches to his AIA contract.   The biggest breaches were going over budget and not giving us notice, and going over the date deadline by 75%!   However, we finished the project except for the punchout (with lots of construction defects), and we received our certificate of occupancy from the city.   Throughout the project, we kept asking for numerous things, including receipts, and lien waivers, all per contract stipulations.  It was like pulling teeth.  He actually gave us a notarized FINAL UNCONDITIONAL LIEN WAIVER even though we had a dispute on the final amount owed.  This waiver was sent to us via email (can be proven), so it is not the actual original copy.  He has since filed a lien on our project.  Any ideas on how to proceed?

Thanks in advance.