Won't release deposit almost a month after rental

Similar to another review, Thrifty won't refund my R4000 deposit almost a month after the rental (booking no ********** ). And just as bad, they won't answer my query regarding this sent to the customer service email. What does one have to do to have the money released? The car was returned in perfect condition (and signed off as such by the attendant upon return), and filled up at the on-site petrol station at Cape Town airport. I have always rented with Thrifty due to their competitive prices, but I don't think they'll see me again after this.