Early Debit Orders

Why oh why does Getbucks think that their will be money in my account for Debit orders on the 23rd of the month if i only get paid on the 25th. Yes getbucks the 24th September is a public holiday but the 25th is a normal worksday and the day that my debit order is suppose to go off as agreed in our contract. WHO WILL BE PAYING THE BACKCHARGES ON MY ACCOUNT? This is not my first transaction with you guys.