Incorrect Debit date

I am currently unhappy, i have always had loans with finchoice debiting on the stipulated instalment date but this month they decided to do otherwise on the account. My payment is due on friday 20th September but for some reason they debited my acc on the 17th and caused a bad record under my name and the 20th is a normal working day. I then called your call centre if i am not mistaken is spoke to Cherly and i asked her why and according to her the contract says debit order will track 3 days before but from my knowledge a naedo debit order waits 3 days before then tracks on the day and if its unpaid on the actual day it will track again. I then when into that contract and under section 6 of payments there is no such its only stated that if the payment falls on a Monday,Saturday or Sunday it will track on the friday before. So i would like to be answered as to why payment was debited on a wrong date