@Coral10
I can see what has happened Coral, you have cancelled a guest reservation! That is the only item on your review page and I would suggest the amount that has been removed from your account relates to that reservation.
When a guest books a listing Airbnb charge the guest immediately and hold that money in trust for you until the guest arrives and they then release it to you. In this instance it looks like it is a mistake on Airbnb's part, when you cancelled the reservation the guest would have been refunded and Airbnb have taken that amount from your account rather than the trust account where the guests payment had been deposited.
Approach them again, and I would suggest via Twitter rather than the phone help. Twitter is quicker and the level of expertise appears to be better. Give the reservation number of that cancellation and explain that this money was never forwarded to you and you require it's return.
I hope this can be of some help to you!
Cheers......Rob