Nedbank inconvenient payment processing system

I received an sms from Nedbank system on my loan payment, stating that they will process the payment on the 17th of Jan, as opposed to the normal Pay day on Monday, I am not even sure why this is the case since that day doesn't even fall on a weekend. They then stated that I could opt out if I didn't want this to be the case, which I clearly and promptly did. To my surprise and major inconvenience, today they processed the payment anyway. The money was intended for other purposes. I am still getting pain on Monday, the contracted debit day, which doesn't fall on a weekend, and I opted out. If this is a problem with their automated systems it's one they should be fixing.