Persistent unauthorised debit order

I am very happy with FNB, however I keep getting a debit order with reference Epi3. FNB told me that these people are a company called Insurance Group. I tried calling them but I kept getting transferred to an extension that is not in use. I stop this debit order every month yet they keep trying every month with a different amount. I make sure I have no money in my account on the day they debit, which is the 28th but am incurring unpaid charges every month, let alone the damage to my credit rating. Please make this nightmare go away FNB.