Sun 1 Edenvale refund complaint

We’ve recently stayed over at Sun 1 Edenvale, I’ve booked for two nights but due to flight delays I’ve asked for a refund for one night. It’s been almost three weeks and it’s still an ongoing argument and still no refund. I’ve explained that I’ve booked online with a travel card and therefor can’t provide a bank letter as requested from them, and also I don’t stay in the country, so it’s not possible for me to get a bank letter. At first they confirmed it shouldn't be a problem since I’ve booked online. I’ve send numerous emails and not getting any feedback or refund.