Vehicle financing

Debit order went off on the 31st although scheduled for the 1st of every month. The debit order bounced and now I'm left to rectify the situation. Called to resolve the issue and wasn't afforded the opportunity to state my case, the consultant who I spoke to kept speaking over me. I referred to my contract:

"Your debit order will be aligned to your salary date, or on the last business day preceding this date where this date falls on a weekend or public holiday, provided that such date is not earlier than your Due Date"

It clearly states that the debit order can't go off earlier than my Due Date and yet it did.