I need help getting my deleted music back into my library. I did not delete it.

How do you proceed in getting your music back if Itunes deleted it? I bought a full album of Florence and the Machine years ago and now it only shows 5 from the whole album. I feel like I wasted my money becasue now I don't have posession to all of their songs. If any of your know how to get my music back, please let me know whenever you can.It'd be highly appreciated. Thank you.