SANI car rental. ********* and disgusting

Port Elizabeth Airport branch staff fairly pleasant but inefficient. Returned vehicle, and handed in completed form giving details of my bank account. More than two weeks later my deposit still not returned. Excuses - They did not have my bank details; they have a backlog. How do I get my money back as they are not interested in helping me. Will I receive interest on my R13,000.00 deposit? I will definitely do everything in my power to put the word out NOT to hire from them.