app music doesn't erase music

Hi everyone,

kind of strange thing happening to my Music App on iPhone.

Simply: it just won't erase the music from the phone. If I try to do it, the music keeps appearing in my Music App, but if I tap on each song, it won't play, but I can still see all my albums and all my songs on the device.

But the worst part is that if I connect iPhone to iTunes, iTunes says that there's no music on my phone but it won't synchronize it!! It recognizes my phone and everything, but the giga left don't correspond.

What is going on?

I'm afraid it's some kind of issue iOs 9.2.1 related maybe? I just updated and all of a sudden this thing happened. I also updated iTunes latest version but nothing changes, it seems I won't be able to synchronize my music...

Any help.

Thank you so much

Davide