Amount owed keeps increasing

I have requested an explanation for this query via email but I'm not getting responses. In March I was told the balance of the account was R500 (and somewhat Rand) and I would settle this in two separate debit orders. On 27 March R300 was debited from my bank account as agreed. On 31 March two R300 debit orders were made to my account which I queried and I was I was refunded R300. To my understanding because I owed an amount in the region of R500 (and somewhat Rands) I have settled the account because in one month I paid R600. Now to my surprise Agnes calls me to tell me that I owe more money. The statement she sent to me mentions a readjustment I don't know about. I queried this with Agnes and instead of a clear explanation my bank account is debited. Please I need an explanation as to why I'm still owing you money. All this time I'm under the impression that I have settled the account and in fact you owe me money. Agnes insists that only two R300 amounts were debited instead of three.