Change of use ie to room and brekfast only and new name.very difficult to talk to booking.com

booking number ***

Hi, we have accidently overbooked for 24th July and need to cancel. How do we go about doing this?

this booking number was for a stay on 5/18 for 1 night for 2 rooms, there is some type of payment error, that very well could be on the hotel's part, I needed