Booking.com not honoring booking

Earlier this month (jAN) I found accomodation advertised on booking.com for R101.00 at ab place called F0ur20 in Midrand, I placed the order and paid for the accommodation. booking.com sent me a confirmation email with pin even and finalized my booking. later they called and said there was an error on the bookings page, and they would like to cancel my booking or have me pay the difference. I refused because they had advertised it for that amount and i paid and they confirmed. They have now cancelled my booking without notifying me or the venue. How do I make them honor my booking at the originally advertised price?