Misdirection

We have recently purchased a home with FNB and the documents signed confirmed when the 1st Instalment was due To Be Scheduled For and it was for the 1st of each new month. We confirmed that the 1st payment was the 1st October 2015, the debit never went off and after we contacted the call centre today we are told by an abrupt agent about 5 minutes ago that the payment is scheduled for the 31st. How can FNB make that our problem to move the dates without our consent as we chose the 1st of each month as we get paid on the 31st only and that we do not want complications if the debit for some reason does not go off on the same day that our salary is released this is not fare.