Hi @Jacqui46,
I'm sorry to hear you got a booking on dates that you had blocked. As @Linda108 said you will need to contact Airbnb to ask them to cancel it for you - here is the guide explaining how to contact Airbnb that Linda had posted in the previous thread.
Just to let you know, I have moved your post here to a new thread so that it doesn't get lost in another discussion and it is easier to find. I have also given it a title, please let me know if you want to change it!
In case you're not sure how to start a new thread - this CC Tutorial gives a step by step guide to starting a conversation in the Community Centre.
I hope you can get this resolved soon.
Kirstie