Customer Asking for a Rework or Refund the advance payment

Dear Sir, I am a software developer firm based in Mumbai and one of our client in Ratlam.(MP) We had a contract to develop a software a 5 months ago. My client have paid me advance payment less then 30% of 100%. I have raise a Sales Order and was courier and need to be sign but my client refuse on that till time and pursue me to go ahead and assure for oral safety. I had complete all of his requirement and data entry begin and complete with online. One of his employee left the job and after a month ago there was a replacement of another employee. in mean time the software got affected a virus which was the result the computer needs to be format and clean. My Client asking to reinstall the software again and inspite of our several reminders to pay outstanding. he is not commenting and threatening to us that I will recovery all of advances if you fail to comply based in PO. My client did not raise PO but he always comment and we have a recorded all of the communications via mail Please advice How to have safety Do I have travel to Ratlam Court ?