horrible service and no proper explaining also not giving customer an option

I have AVAF with Absa and a bond, I received an sms saying that if the debit order date is on a weekend then the debit will be prior to debit order date which will affect my account as on the prior date i will not have enough funds and if I do it will be for other expenses and i called home loans and they did change the Mandate to a ''No " and when it come to the Vehicle finance they telling me they cannot change that??? why is that and this will affect my account i honestly need answers as they telling me that this cannot be changed why is that all these years my debit Oder was not affected even if its weekends/holidays and now it will be affected and nothing can be done .