Refund on a Double charged account

I hired a car with these guys and paid online with their East London airport branch. Upon my arrival to collect the car, the agent who helped me said my payment wasn't reflecting and so he double charged me again, and promised to refund me once confirmation of the online payment is received. It's been more than a month now since I have been waiting for my refund. The worse part is that, they keep on saying today and no one bothers to contact me and let me know when will I get my money back. Worse customer service ever.