Refund still outstanding after month

I booked and paid for a vehicle to be collected at the Cape Town Airport on 11 December 2015. On arrival I was told that a vehicle could not be provided as my license has expired. We were forced to rent another vehicle in my wife's name and had to pay more for the vehicle than the original quote. Since that date I am struggling to get my refund from Hertz. Emails to their customer care are not answered and phone calls result in me being referred to the customer service email account.