Refund Refusal

I have requested a refund several times after I cancelled my contract. I always paid months in advance via EFT and when the contract ended there was a surplus. Cell C keeps insisting that I send a proof of payment from August 2021 in order for them to process the refund. I am failing to understand why they want a proof of payment from 10 months ago. It is not like I paid today and am requesting a refund for that payment. Cell C has been sitting with my money for months and now they want proof of payment for money that has been in their account for 10 months???

In what world does that make sense?