Q: Why won't my 6 plus allow me to delete music

Hello Snowman15678,

I am curious to how you are trying to delete music from your iPhone. It seems that you are going through Settings > General >Usage to do that. Have you tried deleting the music directly from the Music app? All you would need to is navigate to the song within the app and swipe left to bring up the delete option to delete it. Take a look at the article below for more options. 

How to delete content you've downloaded from the iTunes Store, App Store, iBooks Store, or Mac App Store

http://support.apple.com/en-us/HT5772

Regards,

-Norm G.

Hey Snowman15678,

Do any of the songs have the cloud symbol next to them?  If they do, then those are the cloud purchases. You can hide those but going to Settings > Music and toggle off Show All Music to hide any purchases.

-Norm G. 

Hi  Snowman15678,

At that point you should not be seeing duplicates. Because you are, I would recommend contacting apple for additional support. 

Contact Apple Support

https://getsupport.apple.com/GetproductgroupList.action

Regards,

-Norm G.