Poor service from Europcar

I booked a car on Europcar online and paid in full in the beginning of April. Our plans changed and I had to cancel the booking. When I tried to cancel it online it gave me an error, so I emailed them and asked to assist. They rep**** saying that they have cancelled the booking and that I would be refunded in 10 working days. I waited. In the meantime our travel came up, but I kept on receiving reminders from Europcar that my booking is ready and that I can collect from OR Tambo International. On my arrival, I stopped in at the Europcar desk and was assured that the booking was in fact cancelled. I never received my refund. They gave me a phone number that I could call, but never managed to speak to someone. I send an email to Sylvia, who rep**** to confirm the cancellation again. I received a reply from a Lentine who said that I have to cancel online and then I would be refunded. I rep**** again to say I am unable to do so, as it was giving me an error and that is why I contacted them on email in the first place. To date I have not received a new response or my refund. It has now almost been a month.