Double billing for Shipping

I bought a MacBook air Order Number: ********. I was charged

Subtotal $1,231.00

Shipping $13.00

Estimated Tax $99.28

Order Total $1,343.28

I was later charged another $13 and I am not sure what it relates to because the shipping amount was already included.

How do I get the refund Or detail on what this related to?

<Edited by Host, Removed Personal Information>