I would like to terminte my contract with booking.com

Hi

You are looking for "end my partnership ".

Quick version

1. In the extranet, go to the ‘Inbox’ tab.
2. Select ‘Booking.com messages’.
3. Right Pane - Click on ‘See Contact Options’. 
4. Choose Account
5. Now choose TERMINATE
6. Then follow prompts

Those 6 steps are the official quickest way to close account off, once you have your  ducks in a row.

Kind Regards,

Be Safe, Be Well