Never paid severance

Hello. I recently was in a really bad situation. From day one there were red flags but I ignored them, assuming if I did my best at a jobI had accepted, things would work out. In the end, I was replaced by my bosses friend. Turned out I was only an intrim employee, but they had no plans to tell me that when they hired me. They offered me 3 weeks paid severance to resign. I was paid bi weekly and had already worked one week that pay cycle when asked to step down. So that should be 4 weeks pay. 1 week worked, 3 severance. I have only been paid for 2 weeks. I have emailed my old boss to inquire about the rest and there has been nothing but resounding silence... Suggestions?