not returning deposit

I rented a calculator through the company from July '09 to August '09. In the contract, they required $35.00 deposit for security reason and promised to put the same amount back on my bank account 2 weeks after they receive the product. I returned the calculator on 08/07/09 and the delivery confirmation showed that they received it on 08/08/09. It has been longer than 2weeks and I haven't received my deposit back. I e-mailed them twice and had no responses. I called them from 11am to 5pm every 10 minutes on 08/27/09, and I was not able to speak to anybody but the message that they're helping other customers so I have to call them back in a few minutes.