Yoco - not refunding my customer's money and not responding to email queries

I have been using Yoco for the past few months and on 18 September I did a refund for a customer in the sum of R579.00. Two days later, the customer came back to me complaining that she did not receive her refund, that the funds was taken from her account but not refunded. I contacted Yoco online and was told that I needed to provide the customer's bank statement to prove that the funds was not returned to her account. I sent the necessary email with the requested documents and to date am still waiting for this matter to be resolved. I have written numerous emails to Yoco (none of which was even acknowledged) and I had online chats with 3 different representatives of their organisation, each promising to investigate and resolve the matter, but to no avail. A response from them is still forthcoming. All I receive in my inbox is a script of my convo with their agent. Further nothing from Yoco.