Location code received doesn't work

We are trying to confirm the location of our property to add it to Booking.com. On August 21, 2019 we received from Booking.com a 6 digit code by post and when we use it to confirm the location we get a message "Sorry - that code is incorrect". What is more strange: in our Booking.com account confirmation page says that "Your letter should arrive by July 19, 2018"!!!!! Could you please help us solve this situation asap. Is a very tedious and time consuming process to be even more aggravated with errors. Looking forward to hearing from you with a quick solution to this problem. Many thanks, Antonio Paramo