No refund for being overcharged

On 15 August 2024, I was double charged for my monthly premium. I was charged R461.10 instead of R230. When I enquired on 16 August 2024 about the issue I was told that the money will be credited back into my account within 72 hours . However, on 22 August 2024 when I enquired about the money I was told that the credit amount was allocated toward the September 2024 invoice. I’m so disappointed that they decided to allocate the credit amount toward the September invoice without consulting me because I expected a refund and I informed them that I needed a refund.