Fails to Pay for Artwork Sold

This company offered to sell two oil paintings (value R7500.00) on my behalf, and a written agreement was reached in August 2013. Both paintings were sold in January 2014, but the owner, Llewellyn Kruger and his wife Jennie, has failed to pay for the larger painting (R5500). They have had numerous excuses, and does not respond to any of my messages or requests.