Billed twice in two consecutive months

In April I asked MFC to change my debit date from the 15th to the 25th of every month because I was changing employment. On the 15th April the debit was returned due to insufficient funds in the account and was immediately taken to collections. Arrangements were made to collect their monies on the 24th April 2015 and it was collected. On 25th April the debit went off again and I immediately contacted MFC and I was told to wait for 10 days to be refunded but I reversed the debit order though my bank. Now this month, the debit went off again on the 15th and I immediately contacted MFC and was told that the previous request was not completed and that the same amount would run again on the 25th. The debit went off twice again today, stating that my account is in arrears. I need this matter to be resolved and I am demanding explanation of what happened. This is impacting negatively on my credit history and I feel that I have to be reimbursed the 600 rands I was charged for my returned debits.