Unauthorized debit order

There is an authorised debit order called IZIPHI , which debited my account twice in 2 weeks,the amount is R299, I don't understand how FNB can charge me for a debit order I have not authorized. That's complete nonsense. I'm using my own airtime to call them to reverse that debit order then I'm still charged R18 to block it. It's clear my money is not protected with FNB. I'm starting to think FNB is responsible for this IZIPHI debit order. I'm not the only person exeperiencing this.