@Heather193
you are not the only one who has problems with calendar. I have to block days always twice, first time is always unsucessfull. So double check.
Other hosts have blocked days randomly unblocked, it seems it has something about 3 months in advance availability...
You can tell your guests that it is an error and ask them to cancell. They can do it without any penalty and will get back 100% back. If they don't want to do it then you can contact Airbnb , tell them what happend and ask them to cancel without penalty for you. Here is how:
https://community.withairbnb.com/t5/Community-Help/Contact-Airbnb-A-Community-Help-Guide/m-p/16165/h...