Check Service and Support Coverage

Recently I cross check my iPhone 6 Serial Number against the Apple Service and Support Coverage web page (https://selfsolve.apple.com/wcResults.do), the result page shown that the mentioned product serial number has been replaced. The details of the message as follow:

"We're sorry, but this is a serial number for a product that has been replaced. Please check your information and re-enter your serial number. If your information is correct, you may need to contact us."

Anyone who had experienced and encounter this issue previously, appreciate you can enlighten me? ;-)