Bookings.com taking money for no reason

Made a booking through Bookings.com and wanted to change the dates AND upgrade the booking. Firstly so impossible to get through to a call centre/human - only email until I dug up a phone number. They said the booking is through a 3rd party and they cannot amend. Called the hotel - they said to contact bookings.com. This is ridiculous - I am not cancelling I am moving it (where there is availability) AND upgrading. Utterly terrible service