I purchased the SanDisk Ultra 64 GB MicroSDXC Class 10 UHS-1 Memory Card in the week before Christmas for my new phone, and I thought I would use it as my new music player. So I copied lots of my music files to the new SanDisk micro card.
All was well until the week after Christmas when I noticed that all music was gone–totally disappeared. I’m not aware that I did anything that would have destroyed all this memory.
Are the files still there if you connect to your computer via a card reader? Make sure the reader is SCXC (exFAT) compliant. For that matter, make sure your phone is too.