I have an iPhone 5S. I can't get the ring tones I've purchased to sync onto the phone. And, I can't get the ring tones I've assigned to individual contacts to work-it always reverts back to the default. Can anyone help me? It's so Frustrating!

I have an iPhone 5S. I can't get the ring tones I've purchased to sync onto the phone-and most were actually purchased on the phone through iTunes, but then disappear. When I conenct the phone to the computer, all of the ring tones are in my library and the boxes are checked indicating whih ones to sync, but then they don't sync. Also, I can't get the ring tones I've assigned to different contacts to work-it always reverts back to the default ring tone. I'm in ring tone ****!😕