Help! After signing up for Apple Music, 'Media Services' on iPhone is gobbling up all my cellular data despite my settings to not use it I just signed up for the Apple Music service.  I have a fairly large iTunes library.  It did its thing overnight on wifi (or so I thought) and uploaded my library to the cloud from my mac.  Fine.  But today as soon as I left the house my iPhone immediately chewed through 1.5Gigs of data before my carrier luckily shut it down (I have a 1 gig plan).
The usage is all from the 'Media Services' item in system services, but I don't know what that actually is (cellular->System Services->Media Services)

All of the following settings are off and were already off before the data use, what else do I need to do to stop this?   


Settings->Music->Use Cellular Data  (off)
Settings->iCloud->iCloud
Drive->Use Cellular Data (off)
Settings->iTunes &amp; App Stores->Use Cellular 
Data (off)


Could this have anything todo with iCloud Music Library setting, which I think was turned on for me as part of Apple Music?
After some extensive testing and looking at the data usage time period, I have concluded that I was bitten by the 'wifi assist' feature (which is now set to off).   The massive sync of songs to my device from the cloud was actually when I was or should have been connected to my wifi, and was 'assisted' by my cellular connection, even though that sync would not have been allowed given my settings if just on cellular and not wifi.