Why do i have duplicate calendars?

Question

I noticed this morning that I have duplicate calendars showing duplicate events on all of my devices: iMac 2011, MacBook Pro Retina 2014, iPad Air and iPhone 4S. All with latest system updates. Only the calendar for my school events (which I use most actively) shows as duplicated, others remain normal. I followed the instructions on Apple's troubleshooting page: I checked that all relevant services were shown green on their system status page. Then I went to iCloud.com and checked whether on not the calendars and/or events were shown twice there as well. I saw two calendars for my school events by the same name, one with purple color that I remember choosing, and another with blue color that I think is the default color for new calendars, and that which I had not chosen. But check this: The events on iCloud calendars were NOT duplicated, but randomly shared by these two calendars. Meaning some of my school events were purple, some were blue. I have always used only one calendar for my school, the purple one.
Let me recap:
On all my devices: Two school calendars with duplicated events, purple and blue.
On iCloud: Two calendars, purple and blue, but no overlapping school events! Both purple and blue events with no apparent logic afaict.
Now the next step on Apple's page was to contact the telephone support. I submitted a contact request, and after a short while an american lady called me and we started trying to sort things out. I tried my best to explain to her my situation, but perhaps because things were quite complicated, and English not being my native language she might not had understood everything. She asked me if I had tried to delete one of the duplicates. No I had not, because even though on my devices the events were shown twice, on iCloud they WEREN'T, and I didn't want to take the risk of losing anything. I think it was at the moment I was explaining this to her when the line dropped, and she never called back.
Having given up on tech support I decided to try fix this on my on and went back to iCloud. I thought if I change all blue events to purple and then delete the blue calendar, I might not lose any events. So I double-click on a blue event, change the calendar back to the original purple and hit ok. I get an error saying "Couldn't save changes to [event's name]. Your changes to this event couldn't be saved because of a server error. Please try again." I report and hit ok. The event is still blue. I double-click it and try to change the event's calendar again. This time I get an error "Couldn't save changes to [event's name]. Your changes to this event couldn't be saved because it was just deleted by another device." I hit ok, and NOW I see two of the same event, one in blue and one in purple. Well at least the event is now supposedly where it should be. I repeat this annoying procedure to all blue events. Then I try to delete the wicked blue calendar, praying I won't lose anything important. Of course I get an error: "Couldn't save changes to [calendar's name]. Your changes to this calendar couldn't be saved because it was just updated by another device." So I go and try again, it worked for the events. And this time the calendar is gone!
But wait. The events of the purple calendar are now duplicated. So I only got rid of the calendar clone, but I still have events shown twice.
I'm getting way too tired to work on this any futher. Why is iCloud acting like this?

Answer 1

Highlight a song. Press command+r to reveal the song in Finder. Do that for the duplicate. Are they in the same location? You can also check this by getting info on a file and checking its location in the summary info, then check for the other file.
If you have a file in a folder that itunes doesn't control and then add the file to itunes it will place a cpy in the itunes folder when you add the file, leaving the original. Not sure how you ended up with two in itunes but I'd need to know the details of your preference settings.
I don't know about the rest. I have never bought music from ITMS.