xi6-a new from ebay

I have a TCL Google TV that does not have access to the Xfinity Streaming app. I have just returned all of my cable boxes to stop paying rent fees, and I was told the app would work.

Since then, I got a new Xi6-A off eBay and tried to use that. When trying to get the box activated, I was told I would be charged a rental fee. It's my box what am I renting? Do I need to go get another small cable box from the xfinity store?