as mentioned, the billing and support phone support wont be able to help you with this

only way to get this hopefully fixed is by sending in a dispute trough the email adress you received in the ban email.
something like accountreview@blizz
only they have the power to return your accounts and revoke a GM's decision.

Just write them politely that you think you have been banned injust, explain that you are multiboxing which has been deemed legal so far, and perhaps include your HKN script to show them what you are using.