I second this approach. Had a similar problem with a client in the UK two years ago. They dragged their feet for a few months, then gradually stopped answering

I second this approach. Had a similar problem with a client in the UK two years ago. They dragged their feet for a few months, then gradually stopped answering emails and taking my phone calls altogether. I wrote a very angry email saying I intended to sell the debt to a collection agency, to ensure they paid in full, even if I never saw any of the money myself. They replied on the very same day, we negotiated, and I recovered about half the money I was owed by the end of the week. On the other hand, forget shaming them publicly - you open yourself up to accusations of libel - or empty threats of legal action - you simply don't have the resources. The same goes for sabotaging or erasing your code. But debt collection is a very real option.