Do debit orders early without contacting the Customer

I have a loan with Nedbank, my debit order date is the 27th of each month. They change the debit order date as they wish, they have just debited my account on the 23rd, I did not even received my salary yet. What is the use asking clients on which date they want a debit order if they change it as they wish WITHOUT THE CUSTOMER CONSENT.. Im really not happy anotut this.