Unauthorised debit order

This morning i woke up to a sms that came through at 00:39am ( when I was alseep) saying that I have purchased a MY MEG 10 SUBS bundle and that R9.00 will be debited off my account every month. I absolutely did not authorise this and I'm disgusting that this can even happen. How does vodacom let this happen ?I want this to be reversed immediately! I'm completely annoyed. Sunday ruined thank you vodacom!