OVERPAID BILL, NO REFUND

I had a missed payment. On the 30th of November i paid using Paygate. Later on that day MTN debited. Contacted them asking for a refund they said i must email my proof of payment which i did on the 4th December. There was no response as to we have received your proof of payment and money will be reversed into your account within.... hours I get an email that my payment was allocated in my account. I want my money back