Penny I am sorry to hear this.
Hopefully you had clear guest rules in place to state that only guests who had booked could stay at the property, that there should be no parties and noise should be kept to a minimum, and evidence of damage/extra guests, so this should be fairly clear cut for BnB.
What did you do when the property manager told you about the additional guests, campervan etc - surely you would have alerted BnB and told the guests to leave immediately?
Anyway....I thought if you didn't write a review theirs couldn't appear for 14 days?
I would get onto BNB straight away, say that this is a malicious review left because you are looking for financial compensation through the guest deposit and also BnB's host guarantee (I presume to cover damage/extra guests etc) and request it is taken down.