iTunes music library
6 months ago or so, I synced my iTunes music library up with the iCloud.
I really can't exactly remember the sequence of events, but I used to have all my music on my laptop / iPhone - and with several thousand tracks, the memory used to be virtually always full. So somehow there became an option to send to the iCloud. i did so, and note now i have a lot more capacity on my iPhone as not all tracks are downloaded, so plenty of capacity.
However, when i listen to my music now (e.g. a compilation album), the track that plays is not my track! I have many weird and wonderful collections of music, of which I am very familiar with, so am acutely aware of when a slightly different version of a song is played (the artwork shown is also different).
Anybody any ideas what has happened, and how I can get my original stuff back?
MacBook Pro, OS X Yosemite (10.10.3)