We finished the work over a month ago and did not file a prelien when we started the job. The customer paid progress payments but are withholding retainage. What are our options to collecting the remain money.
I your contract was directly with the owner, you are not required to give preliminary notice unless a lender is involved. So in this case, you could still record a lien as long as you are within 90 days of project completion, or 60 days from the notice of completion, if a notice of completion was filed. If your contract was with someone other than the owner, then you cannot record a lien unless you can prove that the owner had actual knowledge of your work.
If a lien is not an option, then you can proceed instead to threaten and if necessary file a normal action for breach of contract, in addition to other causes of action, against your customer. If your contract has dispute resolution procedures, you must follow those procedures which likely call for mediation, arbitration, and/or litigation.
Absent specific procedures, I generally recommend first sending a demand letter and then filing a lawsuit if they ignore the demand letter.
You still have a breach of contract claim. If you're not paid, you should pursue a collection matter in the courts, depending on the amount owed. You may be able to recover attorneys' fees, costs and interest under California's Prompt Payment statutes. Good luck.