how to Cancel AppleCare

Why do you need to cancel it? I don't think that is possible. It's an extended warranty so I don't think anybody has ever even thought about it being something needing canceling. If you don't like it then just don't use it. I doubt you can get it refunded under normal circumstances. If you really, really have come up with some unique reason you absolutely must have it canceled:

iTunes [Store] Support - Use this form for assistance with account and billing, code redemption, or purchase questions - https://ssl.apple.com/emea/support/itunes/contact.html

You can't. Apple Care is a one time purchase. You've paid for it already, you get it for 2 years from date of purchase.

It is not an ongoing subscription you can cancel.

Why do you need to cancel it?