First, I wanted to let you know that while checking your account, I noticed that the invoice has cleared. I have refunded the unauthorized purchase order "M2XJD233S5", for you. You will see a credit of €11.98 posted to your account shortly. You may need to sign out of the iTunes Store and then sign back in before you see the credit in your account.
Now to help you regain access to your account again. With the information you provided, I have enabled your account for you. As a part of the enabling process, it is necessary for us to reset your password. To access your account, you will need to also reset your password again from your end. I'm sorry for any inconvenience, if you have already changed the password, Bram.
Additionally, if you have not done so already, please also change your security question as well. Changing the password and security question will help to prevent anyone else from using your iTunes Store account to place orders without your knowledge.
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I know you're concerned as to how someone was able to access your account details Bram, and although I cannot speculate on how the information was obtained, I would like to provide you with some tips, to prevent this type of issue from occurring again in the future.