Deducting debit orders before salary date

I have a standing debit order for the 27th with Capitec. Today, on the 17th, somebody paid money into my account for personal reasons, and Capitec deducted the debit order immediately even tough my salary is only paid on the 27th. This is unacceptable because I signed for debit orders on my salary date. Why do they take money before salary date? And I am sure if aby debit orders go off with no money in he account they will charge me!! Why not wait for my salary and dates as contracted?? I have seen that some companies take the liberty if deducting debit orders sooner in Dec. But surely you can wait till salary date!!