Early debits

Can someone tell me why African Bank debits my bank account before I get paid? Ok yes I do get paid on the 25th of every month, my salary could possibly be in on the 24th. At the time of the debit order it wasn't in yet. What hidden clause probably written in fine print is your defense Africa Bank? If I have no money in my account and you try to debit then I will be charged for a failed. Be fair to your customers.