Purchased song is on iMac and iPad, but cannot get it on iPhone 5S.

I purchased a song several months ago, I believe with either my iPad 2 or my iPhone 4S (which I no longer own), and while it is in my iTunes library on my Mac and is on my iPad, I cannot get it onto my iPhone 5S. My iPhone is set to "Show All Music", I have synced my iPhone with iTunes on my Mac, and the 25 other songs I have purchased are all on my iPhone, yet this one will not transfer. When using my iPhone to view the song in the iTunes Store, it shows as "Purchased", and is ghosted, so I cannot download it directly to the iPhone. I have tried every means of resolving this issue, short of restoring my iPhone, as I have spent hours on here and searching the Internet in an effort to fix this problem. I don't know if this may have anything to do with it, but my entire Music Purchase History in the iTunes Store, save my most recent purchase, is empty; my video purchases are all intact.

Any assistance would be greatly appreciated.

Thank you,

Sam