Deposit Not Paid Back 16 Days Later

My sister returned the rental car from Avis Marshall Town on the 24th August as per their agreement. She was then informed that her deposit will be paid back within 5 - 7 working days. On the 10th day she went to their offices to enquire as she had not recieved the money. She was then informed that the form on which she had completed her banking details is missing and was asked to complete another form. She was told since her money is over due, she will get the payment withing 3 - 4 working days there after. Today is the fifth day and still the money hasnt been paid back and there is no communication.