Accidentally deleted song from iTunes library - not available in purchased items.

Hi

I accidentally deleted a song from my iTunes library when trying to remove it from a playlist. The song was originally purchased using the app on my iPad, but when I tried to download it again from "Purchased", the song isn't there. I've looked under the "All" tab and the "Not on this iPad" tab. There's nothing available under the second tab at all and I haven't hidden any purchases. I can't even buy the song again from the iTunes store as it's showing up as already purchased. Can anyone help please?

Happy new year!

Ewan