I have an unauthorized charge on my account

I recently bough the iPhone X, and I got charged correctly for it, but 2 days later I have gotten a second charge of almost the same price (it is a few bucks less, probably due to currency exchange fluctuation because I paid in euros) but I dindn´t make a second order, and in my account only 1 order appears.

What can I do to get this shorted out if I´m out of the EEUU and can´t phone customer support?

Thanks.