Wrongful debit

My bank account has been debited today (11 December) and as per our loan repayment agreement with Nedbank its supposed to be debited on the last day of the month. <br> <br> Yesterday I received a sms stating that I should fund my account, that's when I decided to call Nedbank and they claimed that they sent me a sms on the 16th of November which I never received. I was thereafter reassured that the debit order will go off on the last day of the month but to my surprise I wake up to a debit and bank reversal sms meaning the debit has bounced due to insufficient funds as I do not leave of my cheque account. <br> <br> I am very disappointed as this is going to affect my profile negatively.