Customer refuses to pay or acknowledge we do work for him.
You really should retain a construction attorney to review and evaluate your legal position based on the contract and pertinent documents. The right to be entitled to file a mechanic's lien is set out in Texas Property Code Chapter 53, and you really need to make sure that if you file a lien, you have properly and appropriately done so.
Filing an invalid lien could subject you to liability under the Texas Fraudulent Lien Act, and you could be liable for statutory damages of $10,000, or actual damages, whichever is greater, plus attorney's fees. Facing such a claim would add insult to injury.
You should consider preparing a letter to mail by certified mail, return receipt requested, to the customer to set out the facts and to demand the relief that you want. Make sure that your letter is professional and business like as it may be evidence later.
If your lien is legitimate, and your customer still will not pay, consider filing suit. If your claim is less than $20,000, you may consider filing suit in small claims court, although doing so will not confirm or enforce your lien. It is a lot cheaper and quicker.
If you wish to enforce your lien, you will have to file in district court, but that will require that you retain an attorney.
Good luck.