Transactions debited on a Sunday

Every month i have to wait for most of my debit orders to go off only on the next working day if my debit date fall over weekend or public holiday. Last month my account went into debit and money was transferred into my account but my debit order was returned because no money in bank when debit go through the night. This week is long weekend so on Saturday i paid my pretorium Trust and bought electricity because i know i transferred money from Nedbank to Fnb and it will only show Tuesday night because of public holidays and weekend. Thare was enought money fir mfc which installment normally go triugh despite the day. Huge was my surprise to see that some if debit order went through on a Sunday? Now myaccount is overdrawn and there is nithing i can di now i already transferred the miney out of my other account. I know my debit orders will be returned because Fnb have no hrace oeriod like Nedback to give you up to 36 wirking day hours to bring account in good order. Previously i had my account overdrawn and paid the honouring fee but now adays no grace if account us overdrawn then bank send it back immeduately despite if yiu have nade arrangements. Poor customer service