This is why I don’t take walk in work anymore. Most are deadbeats or cheapskates.
Seems to me a couple more phone calls are in order. Otherwise consider yourself ripped off and give it to the debt collectors. I have been ripped off for a lot more than that and it just sucks. It is one of the hazards of self employment. You have my sympathies and I have been in the same boat many times.
Visited the website and sent an email. Hope it helps!