Rental application deposit advice needed

I have applied for a rental property, and the application process has been strange from the start. The 'agent' phoned my previous work asking questions about me, but would not identify where they were calling from until the end of the conversation despite being repeatedly asked. They did not phone my current place of employment. Now I have just received a text message telling me that my application has been approved, and requesting that i pay $550 deposit otherwise they will give the property to someone else (what is the legality of this type of demand?) I have phoned the contact number noted on the message, and have been informed no one by that name works at the agency. How to proceed?