Second time all my music has disappeared

This is the second time this has happened, all of my music on my phone has just totally disappeared!

My phone is a 128gb iPhone 6s Plus running 9.3.1

First time it happened i was listening to my music via my headphones, i paused to talk to someone, pressed play and nothing happened, had a look - ALL my music had gone. Everything else like photos/contacts etc were still there, only music was deleted. Unsure what ios i was running then, it was about 3/4 months ago not 100% sure.

Second time this happened was saturday 30th april, i got in my car for a weekend away, went to play music over bluetooth - GONE again. Every track, but again all my photos etc still there and phone working perfectly fine.

I came home today, plugged my phone into my pc and started up iTunes, all my playlists were still there, but all the music had disappeared.

I really cannot for the life of me think what is causing this, its taken me about 3 hours to put everything back on how i want it.

Can anyone shed some light on this for me?

If it happens again i may have to send the phone back to my network provider