Hard earned Money - FNB Unauthorized debit orders

For the second time I am getting a Mzansi unauthorized debit order on my account. These people have used my ID number as their reference number. First debit order was R109.00, they have clearly increased the debit order amount this month to R135.00 of my hard earned money. I do not understand why it should be my responsibility to reverse these debit orders as i have not authorized them.