I'm a contractor for a multifamily project, and we pass to file a mechanical lean deadline. Our deadline was on August 15. Is there another course of action to receive payment?
You really need to retain a construction attorney to evaluate your situation and to provide advice.
The deadline for filing a claim on the retainage may still be available. A retainage claim would at least keep the door opent to full payment.
You should write a letter by certified mail to your customer to demand payment. Attach to your letter your unpaid invoice(s) and photographs of your completed work. Make sure that your letter is business like and professional as it may be evidence later.
If your letter is ignored, consider filing suit, using your letter as evidence.
Good luck.