WP Office X6 Installation Problem

I recently purchased WPO X6 Standard Upgrade from Amazon (not a 3rd party). I have WPO X4 Standard installed on my computer. I'm trying to install X6. I entered the serial number from my new disk. Then it asks for the serial number of my X4 version. I typed it in and got a message saying the serial number was not supported for upgrade. I went to my Corel account and cut/pasted the serial number I entered into my account when I registered the X4 Standard version (which was the same as I had typed). I still get the error message. Has anyone else had this problem? Does anyone know how I can get past this? I cannot figure out how to contact Corel to get this resolved. Help, please! Barbara