Answers come from other users who have encountered the same problem and solved it, not from Apple personnel, so you have to be patient and wait for someone who has experienced the same problem to come back to you on this. Sadly it may also mean you don't get an answer. (I found your query when searching for help over iTunes continually re-opening when I close it down, ending up with my having to force a close using Task Manager so afraid I can't offer any help either).
Edit
Another answer in my search led to this thread which may assist you
How to stop iTunes from opening up on Windows startup?