Sanlam December debit order date

I don't understand why I have to go through this with Sanlam every year when it comes to December. Sanlam sends me an sms to say I should confirm or decline that they can debit my account on the 15th and I reply on the number they say I should sms to and decline that as the 15th is not my pay day, this morning when I wake up, they tried to debit my account. last year the same thing happened and I called to let them know that under no circumstances should my account be debited before the debit order date I gave them. I honestly don't understand why I had to send an sms to decline the debit date of the 15th if they still sent though the debit order.