Q: iPhone has deleted all music from device

Did you restore your phone before that?

Did you check that Apple Music is disabled in Settings/Music?

To make sure that this is not software related, set the phone back to factory settings by following the steps in this article:

Use iTunes to restore your iOS device to factory settings - Apple Support

When you set it back to factory settings, did you restore from your latest backup or did you start without using it, in case it contained corrupt data, that was causing this?

Did the phone reboot itself before you noticed that the music has been erased?

Did you sync the music via iTunes from your computer and has the music been bought in iTunes?

Did you already check this discussion and the answer given by donpretlow?

My debit card was declined so they wouldn't let me play anything including what I already paid for. Now it looks like they totally deleted all my songs.And to think I paid them for apple music so they could keep my songs in the cloud and take them whenever they want.Tried paying with gift card but don't work.You can have them apple.I went from fan boy to hating anything to do with apple.

@Newcuyote:

Sorry, but the Apple Music subscription can not be paid via gift cards. After your subscription has been canceled, music you did buy from iTunes before you subscribed to Apple Music, can still be downloaded again for free:

Download your past purchases - Apple Support

Sorry, that this did not work either.

Did you check these articles as well?

Suddenly all of my songs from my iPhone vanished. I didn't connect it ...

Apple acknowledges reports of personal music files being deleted ...

Yes, syncing the music again to the phone, and hoping that this does not happen again, would be the best solution at this time.

Did you check the "Other" section in the status bar when you connect to iTunes? Did it increase by the size of your music library on the phone after the music has been gone? Usually it should be around 2GB at most, any bigger size could indicate damaged files on the phone, which in your case could be your music files.