Help! After signing up for Apple Music, ‘Media Services’ on iPhone is gobbling all my cellular data despite my settings not to 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 I uploaded my library to the cloud from my mac. Beautiful. But today, just out of the house, my iPhone immediately chewed up 1.5 Gigs of data before my carrier shut it down (I have a 1 gig plan).
Usage is everything from the ‘Media Services’ element in System Services, but I don’t know what it really is (Cellular-> System Services-> Media Services)

All of the following settings are disabled and have already been disabled before using the data, what else do I need to do to block it?

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  • Settings-> Music-> Use cellular data (disabled)
  • Settings-> iCloud-> iCloud Drive-> Use Cellular Data (disabled)
  • Settings-> iTunes and App Store-> Use Cellular Data (disabled)

Could this have something to do with setting up the iCloud Music Library, which I think was enabled for me as part of Apple Music?

After some extensive testing and looking at the data usage time frame, I concluded that I was bitten by the ‘wifi assist’ feature (now set to off). Massive syncing 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, although that sync would not have been allowed based on my settings if only on cellphones and not wifi.

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