Unauthorised Debit Order date

Please explain to me why you did you debit my account on the 18 May 2018 without my authority , now my cheque account has an unpaid debit order, I get paid on the 20th , when did I authorize a debit order to go off on the 18th? You need to pay back the R178.56 on the 30th May 2018 an unnecessary unpaid debit order on my account and I need an apology letter , you need to contact the bank and explain the mess you did

Regards Salani