Hello @Nigel92,
One possibility is that the "Advance notice" setting may be set to something like 7 days.
To check if this is the case click on "Host" and select "listings" from the menu. Then click on the listing. then click on "Availability". Then check the "Advance notice" setting in the "Reservation preferences" section. If it's not what you want it to be click on the "Edit" button for that section and change the setting.
You could also try to manually unblock dates up to the 24th. Go to your calendar and click on a date. then click on "Available" and "Save" in the box that appears on the right. Repeat for other dates to be unblocked.
For information on ways to contact Airbnb support type "contact airbnb" in the "Search the community" box on these forum pages where you posted your question. Scroll down a little in the list of suggestions that appears and click on the "Contact Airbnb: A Community Help Guide[UPDATED]" one. That lists phone numbers and ways to contact them via Twitter or Facebook.
Steve.