Failure Booking.com system

Yesterday evening I booked accommodation via booking.com and after entering my card details, within minutes I was sent a message that the booking was declined and I would get a refund. I then booked alternative accommodation. Early this morning I see the booking is now confirmed and payment is being made. So far it’s been impossible to get hold of booking.com to correct their error. I’m trying many avenues to get a refund. Very frustrating.