I have an iPhone 5s that I use for streaming Pandora in my truck on a business account that has a large, but not unlimited data plan. 3 days ago I noticed iCloud Match bumped up the limit, so I signed up.
This morning my iPhone started reporting "low storage" error! I turned out it pulled 10GB of music over LTE. The same symptoms like everyone here; repetitive downloads that filled up the phone for now reason.
Called Apple and spoke to 2 people. (Not sure if the 2nd guy I spoke to was actually Level 2 tech or not) To his defense he called me back 2-3 times as my backup cell was dropping the connection. We tried everything, disabling LTE, disabling iCloud Music Library, Automatic Downloads, etc etc.
POSSIBLE FIX:
This 5S was a clean install, with not a single local copy of my iTunes playlist song. It kept on downloading UNTIL we logged off from the iCloud and iTunes accounts THEN rebooted and finally signed back into the before mentioned service.
CAUSE:
1. Looking back, everything was good to go for 2 days. Last night I looked at my mac mini's iTunes and noticed a lot of songs with the crossed cloud icon (not eligible for upload). 
As these were legitimate songs I selected quite a few of them and "forced" the upload to the cloud. Not sure if this started the problem or not...and not sure why these songs can't be uploaded either. These are mp3 files not videos.
* At the same time my personal iPhone 6S+ (on IOS 9.0.2) did not start any automatic uploads. This phone had some locally stored music and I managed to download a few songs to the existing songs from the cloud without any ill effect.
APPLE should be working on this issue as if I had a 128GB phone, I would have used $900 worth of company data this month! Good thing a 16GB 5S got filled up quick and drew my attention.
P.S. I'm thinking about uploading 9GB of videos to use up available space on the phone and try to force the above mentioned songs to sync.