Fnb unauthorized bank transfers

FNB made an unauthorized transfer from my savings pocket to a private Cheque account I closed a year ago ,I went there to try and resolve the issue and I was told the bank would contact me and send an email explaining the transfer but never received any email or call ,both the lady and the gentleman who assisted me even admitted themselves that I was supposed to be notified first and and made aware of all these charges and the accounts existence . The best fnb could do is send me a text saying FNB:-) We confirm having deducted R6394.02 from acc no.18743 to acc no.18735 to reduce arrears. FNB DIV FRB LTD. First of all I wasn’t aware of these arrears and The account is not even there on my banking app ,I only see one account my easy savings account . Wasn’t I supposed to be notified about any transfers scheduled on my account ,wasn’t I to give consent first ? I’m so furious as my money is gone and they are not helping me in any way ???