unauthorized purchases

At 2AM I received an Email stating that my CC had been charged $25.71 for a mobile App that was originally an App I only used on FaceBook. I did not-nor WOULD NOT buy "game chips" for any of my Apps, facebook or otherwise. I went directly to my account and deleted the CC information linked to my ITunes account but wznt this charge REMOVED!! I am the ONLY one with access to my device, and I can assure You, I did not make this purchase!! How do I get a refund?