The first step is to hire an attorney to draft a demand. I hope your contract had attorney fee provisions. If they don't pay you after the demand, then you sue.
Lien strategies and suit issues are complicated and you should contact an attorney to discuss the issues and costs. If you don’t know of any attorneys, contact people you know and trust for referrals. If you have no referrals you should review the attorneys on this site or contact your local bar association for their referral program. If you cannot afford full representation, then you should consider limited representation where the attorney is there to advise you on forms, strategy, and your rights and you proceed to file suit or defend. Our firm has assisted clients in these limited representations and it is less expensive than full representation. Feel free to email to discuss further.