You have done the work. You provided materials and or services but you haven't received full payment. Many calls, emails, and text messages haven't resulted in a final payment. And now, the person who owes you money is screening your calls. What will you do?
If you hire a debt collection company or lawyer, you will have to pay them money. What if you keep trying? Be creative. Would you settle for less?
Depending on, among other things, the facts, amount in controversy, and the collectibility of the debtor, you may find a lawyer willing to pursue your claim on contingency. You would be responsible to pay out of pocket costs, but your lawyer gets paid if and when the money comes. It's nice. Woods Law, PLLC has successfully helped multiple clients to collect their money on a contingency basis.
What will you do differently having gone through this experience? If you are a contractor, are you using the Utah State Construction Registry https://secure.utah.gov/account/log-in.html and timely filing preliminary notices? Are you licensed? Are you using written contracts consistently even on small jobs? A written contract is professional. Do you require half the payment up-front? What can you do to limit the likelihood this will happen again?