I never let someone screw me out of what I am owed no matter how small the amount. In your case the amount is not small. I would tell them to pay within 3 days or you will take them to small claims court. A threat is usually enough. This worked with a car dealership who tried to cheat me out of 500 and a realtor who pulled a fast one and I ended up paying a extra 1k in commissions. After closing I gave her 3 days to give me the money before I went to the realtor board and blew up on social media.

