Put down lost booking account which is used for a fraud

Hello, here's a complicated issue which we encountered:

Our old account access is lost, but somebody got access to that account.

This person is listing our property, accepts money from our customers, when they want to book and pay in advance, and we have to deal with customer dissatisfaction, when they ask us to return the money which we haven't received!

What are the exact steps to put that listing or account down?

Where should we write/call, and which documents should we provide?

Thank you