Hello @Marcia72,
Did the guests that have the old codes make their booking before you entered the new codes on Airbnb?
Guests get their information about the listing as it was at the time of the booking.
Guests who book after you entered your new codes on your Airbnb listing should get the new codes.
If this is not happening then verify that the new code is still entered on your listing and contact Airbnb if it is.
Information on how to contact Airbnb can be found in the "Contact Airbnb" article in the "Community Guidelines" post that you'll see if you click on the "get support" link on the main page of this community forum.
Steve.