I went through almost this exact scenario last year with a full website redesign. Client ghosted on a 42K invoice. Here is what actually worked for me and what I learned the hard way.
Step one is to send a formal demand letter via certified mail, not just an email. The letter should reference the contract, list all deliverables completed with dates, state the amount owed, and give a deadline of 10-15 business days. Mention that you will pursue legal remedies including attorney fees if the contract provides for them.
Step two is to consider whether you have any leverage through the work product itself. If you built software or a website and retained access credentials, you may be able to take it down. Check your contract first, as some contracts transfer ownership upon creation rather than upon payment. In my case, the contract specified that IP transferred only upon full payment, so I was within my rights to disable the site. The client paid within 48 hours.
Step three is filing in small claims court for amounts up to 10-20K depending on your state, or regular civil court for larger amounts. For 57K you would need regular court, but many attorneys will take these on contingency because breach of contract cases with clear deliverables and signed agreements tend to be strong.
Going forward, always use milestone payments. I now require 50 percent upfront, 25 percent at midpoint, and 25 percent on delivery. Never again will I complete 100 percent of the work before seeing payment.