Vantiva Device

https://www.google.com/search?q=Vantiva&rlz=1C1CHBF_enUS937US937&sourceid=chrome&ie=UTF-8 

What is the exact make and model number of your router / gateway device ?

Ok so I don't think it's what I thought it would be. If you had an XB8-T, it is manufactured by the Technicolor Company, which is now Vantiva. So I was going to suggest it's likely to be your very own gateway device. We've seen this many times before here.

So, is your WiFi locked down well ? Is the gateway's built-in MoCA feature enabled ? Is there a MAC address associated with the Vantiva device ? If you see one, cross-reference with your XB7 and all other devices on your home network and see if it's something of yours.