Unable to disconnect device from WiFi using the XiFi app

I have a Kindle that I can not pause using the WiFi app.  It shows it's paused but is still connected and you can see the usage on the network meter.  I tried chatting with an agent who disconnected the chat due to the restarting of my modem.  Working with Comcast is frustrating and honestly, I think they do not know how to resolve the issue.  Does anybody know how to resolve this issue?  My grandson uses it after bedtime.  I guess I'm back to taking it away instead of using the snazzy WiFi app.