Have Bookings.com increased their commissions

We received a e-mail from Bookings.com which I have copied and pasted below, informing us that we owe more money on booking that they have already charged us a commission. Is this common practice, why were we not informed of this before. 

Below is what I received from them.

“We would like to inform you that a new invoice has been issued today. To view this document please log in to your Booking.com extranet, and go to the finance tab / Invoices.”

Would appreciate any light shown on this. It’s approx €350, this is for the month of August 2019.