Insurance Busters Terrible Service

I received a call from Insurance Busters in July 2018, they said they could save me money by reducing my loan insurance, they sent me a quote and said they would cancel the current cover and once this is done I will pay 664 a month saving me R1000. Since then I have had no correspondence from them, they did not cancel my current cover and started debiting my account. I am now paying my current cover and they debiting me. I have called them numerous times asking to cancel this debit order but they still debit me. I have to reverse the debit every month which means it effects my credit score. Terrible service dont use them