A long time ago I got windows insider. I set it up but then decided I didn't want it as I hered it was buggy. I woke up and saw an update installing and want to know how to cancel it.
I had a similar issue, but with Maps, updating and wouldn't cancel. I'll tell you something to try, might work here too.
Turn off all your internet connections, Cellular/WiFi, then restart your device, doing a soft reset (Holding Volume down button). When the device boots don't turn any toggles on. I think the device will tell you that the update can't be downloaded/installed...Try it.