Nedbank did not debit my account and now blame me that my life cover was not paid

I have just received an email from Nedbank insurance telling me my account was not debited, despite having sufficient funds available in my bank account and now my life cover was not paid. This situation has caused some inconvenience as now they telling me that my life cover will lapse, and I would appreciate it if they could investigate why the debit did not go through and resolve this issue promptly.