Please address my query in full

I've been querying a refund for a whole month and I'm not getting any joy. On 23 June I settled my African bank debt. Because I was on debt management, IPDA also debited my account on 23 June and allocated payments to African bank on 02 July. This caused an overpayment because I had already settled the same account on 23 June. On 10 July African bank refunded R9234,56 to IPDA as the account was overpaid. I've been trying to get this refunded to me and every time I query it I'm told that there is no refund due to me. After a lot of back and forth mails, on 03 August the IPDA paid R6,187.04 into my account. I want to know what happened to the difference between R9234,56 and R 6,187.04? Surely they owe me an explanation!