Definitely contact Booking.com directly through the Extranet - you will find a local call center number which you can phone and request any changes and they are able to open your listing.
I am on Airbnb (only good for high season) and have been with Booking.Com for 6 months. I was getting up to 3 - 4 bookings a day but that is now majorly
You need to contact them via extranet by sending them a message or call your account manager.
Definitely contact Booking.com directly through the Extranet - you will find a local call center number which you can phone and request any changes and they are able to open your listing.