FNB Changing Debit Order Dates without my consent.

I just got a message that my FNB Personal Loan Debit order could not go through (es, because my debit order already went off on the 25th of November as it is supposed to go off.) and will be deducted with the next run, next moment I get a notification that my Personal Loan payment has been done. How can FNB change a debit order date that is supposed to go off on the 25th without my consent? Please explain.