LOL. Just LOL. I have no problem with música tastes but wow alot of people don't buy música and tu still do? xDD
Whatever nice job supporting the artists. If tu wanna buy it. I would suggest downloading it first and if tu wanna support the artists then buy it. o else you'd have this problem like you're having now. This is the reason why I do not use iTunes.
Read this: It even says here tu should backup your iTunes música because somehow they get erased.
When I bought this new Vocaloid album on iTunes, one of the songs got erased but to get it back, I just held the power button and slided to power off and when I turned it back on it was there. If that doesn't work, I guess tu could just try to use iCloud, like if tu backed it up? I usually back my iTunes biblioteca up with my iPhone and iMac so if I lose anything, I just connect it with my computer and I get it back. Um, well, I guess if its not in your purchased lista either, try searching the song up again and see whether tu ahve to buy it again o tu can just tap download again. :I I'm not sure, try contacting Apple. Here's the link to the lista of ways tu can contact Apple: