Cannot active new gateway ARRIS SBG8300

Code:[Edited: "Personal Information"]:E1600:COEM

Trying to activate a 3rd party gateway through the Xfinity app.  I believe I am doing everything correct.  The new modem sees the network and the app seems to see the modem on their end.  It comes up with a generic error message and tells me to try again.

This is a used modem which I didn't think about until now but I'm wondering if this modem is still linked to another account somewhere.  I did a factory reset on the gateway but this did not change anything.  If it is still linked to another account is there anything that can be done about that.  Or do I need to return it and find a different one.

Also, Is there anything else I can do on my end?  

I still have the white XFI gateway but I want to own my modem to get rid of rental fees.  Do I need to deactivate the XFI gateway before I active my gateway?

Error message states:

Sorry, That Didn't Go As Planned

Please try again.  If the problem persists, text an agent for help. 

I clicked the link and it gives me an error code (the one I posted at the top) to text to Xfinity.  It then tells me no agents are available and to call for assistance.  Thought I would try here before calling.