Unauthorised debit order from Old Mutual

Hi, I received this sms from FNB FNB :-) We have noticed that a new debit order(s) was paid from account ending...5395 on ********** 2: R250 Ref. Oldmutcol ********** ********** 701; If you are unaware of this debit order(s), contact Telephone Banking on ********** or your banker for further assistance. Alternatively, visit your nearest branch. Ts&Cs apply. FNB a div of FRB Ltd. I never gave Old Mutual permission or my banking details to take off a debit , so how did they get it right to take money out of my account ? Now FNB says I must pay to stop / reverse this ???? PLEASE SENT ME THE MANDATE THAT AUTHORISED THIS TRANSACTION ELSE IT IS ***** !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!