Who or what is charging me ?

I have an online banking account , so when I purchase something for my game on my iPhone , I immediately go to my online banking account to see if everything is alright , and that’s when I notice my balance isn’t what it’s supposed to be after making that purchase , they charge me for the item , which is fine , but they’re taking out more . What do I do , or who can I contact ? This has been happens every time I buy something for my iPhone games . But now it’s starting to irritate me . Don’t get me wrong , I know there’s fees for things , and I don’t mind that , I would just like to know who’s doing it because I called my bank and she said that they don’t charge to use my online banking card . Please , help me . #dazedandconfusedincalifornia . Thank you .