You do not own any digital music, you own a non transferable license to play back on one or more devices which can be revoke at any time. If you want to "own" music then you will need the physical retail copy on Vinyl, Tape or CD/Dvd. You still won't actually own the music, but you will at least be able to sell the version you have, as is (you cannot sell off bits of it), and you will have the right to back it up "safety". You are not allowed to duplicate and sell that.
Since playback rights are sold to commercial companies like Apple, Amazon, Spotify, etc.. When they loose those rights or decline to renew them then all copies, include those on user's devices must be removed.
I was going to add a lenghty section about my issues over Copyright laws, but we will leave that for another day