Booking.com not giving me authorisation letter for my free refund

I had cancelled a booking with BOOKING.COM which was a free cancelation, they said the refund will take 7 to 15 days. After seeing that days are going no refund i called my bank, they said yes the money is there pending the need authorisation letter from booking.com, They are not send the letter , 4 days ago I called customer service who said they are sending request to finance and 4 days later no responce , i again called today was on the phone with cistomer service for an hour still responce was i have sent request to finance, I am very frustated becouse my money is just sitting at the bank and i need my money , I dont understand why they are refusing my money to be releaszed, I even went to confirm with the establishment where I booked and they confirmed that they dont have the funds i must follow up with bookings.com and I am stuck now becouse how will i get my money