We just received a "demand for payment" for services to a property that we sold 3 years ago. We did not receive anything from them prior to the nasty letter demanding payment and a threat to turn it over to a collection agency. On August 8, 2004, I cancelled the service to the address 16857 E. Napa Drive, Aurora, CO. Our bill was paid in full at the time I cancelled it. What is the best way to handle this.