iTunes Store: Associating a device or computer to your Apple ID - http://support.apple.com/kb/HT4627 - In connection with, "When you turn on iTunes Match or Automatic Downloads, or when you download past purchases on an iOS device or computer, that device or computer becomes associated with your Apple ID." "Your Apple ID can have up to 10 devices and computers (combined) associated with it. Each computer must also be authorized using the same Apple ID. Once a device or computer is associated with your Apple ID, you cannot associate that device or computer with another Apple ID for 90 days." - Additionally instructions for "Removing an associated device or computer from an Apple ID"
If you think you're in the clear as regards to the above, contact Apple:
iTunes Customer Service Contact - http://www.apple.com/support/itunes/contact.html > Get iTunes support via Express Lane > iTunes > iTunes Store