Arris TG862 Telephone not working. Can firmware be updated to fix this?

I purchased the Arris TG862G/NA-8 gateway from Amazon back in January 2014. I used it for a couple of years sucessfully with Comcast. I switched to a competitor with better pricing and now I am trying to return to Comcast/Xfinity and still use the same gateway. It is on the approved list, no one has stated publicly that it will not work. I bet Comcast supports thousands of these gateways and just does not want to allow my personal device back on the network with full functionality. Please allow me to use this device again or announce this device is not supported and remove it from the supported gateway list.

Hi Contigo, the information that ComcastAndrew shared is correct the device is Comcast equipment and should not be used on another account without our permission. I know you purchased the equipment on Amazon and have used it in the past but we do not support equipment that is listed as lost/stolen in our system. Also we don't sell out equipment, so it would be best if you were to go and purchase another modem that's not Comcast branded or you can always go into a local Comcast service center and pick up a new modem. Feel free to reach back out to me here for further assistance or if you have any questions or concerns regarding obtaining a new modem. Have a good day. 

How can a person check the model and serial number are clean before purchasing a used device?

When companies are serious about being Eco-friendly they will use maintainable, upgradable devices and facilitate consumers ability to reuse/recycle devices. Most devices are in landfills shortly after purchase. Please share this with decision makers. Thank you.