Deposit refund not processed

We rented a car from 25th to 27th in Cape Town Int Airport. A deposit of approx 6k was deducted due to the fact that we used a debit card and not a credit card. We were told the deposit would return in 15 business days. When we called we spoke to Lauren and Marlin.we were told they captured the incorrect card number and would escalate and correct, we've sent emails (to customer care) and received no response. To date no amounts have been refunded.