Why have I been charged money?

hi there,

i have been charged 20.98 for unknown reasons. I recently checked my bank account and it says that 20.98 has been taken or for itunes. I did not buy anything on iTunes or AppStore and hope this issue can be resolved. I am a college student in galway city and money is a very tight situation for me at the moment. I really hope this is resolved and I need that money for transport costs home at the weekend.