Wrong invoice amount!

Hi, I am a new host on booking.com. I have only hosted one person for one night from Dec 12th to Dec 13th.The client paid $36 for one night without commission fees of $5.40 as indicated on the booking details. The other booking was no cancellation and no show for dec 24th to dec 26th. Booking.com is however charging me for both clients. I do not agree with their billing and was wondering how else to contact them directly.