Booking is constantly transferring its commissions back to our account

Hey, may be there is some one who had the same problem?

We have ordered payment collection from Booking, so all incomes are collected, then deducted by Booking commissions and transferred back to our bank account. That's good, but when the month is closed up. Booking is transferring to us also the amount of his commissions and then we have to transfer the same amount back. It is not good at all. Taxes and etc. We have write a dozen of letters to Booking but nothing changes... Does somebody has an advice?