Nedbank insurance overdraft insurance debit orders with no overdraft

Nedbank insurance/ Nedgroup life has been debiting my current account for 12 consecutive months for an overdraft facility insurance after settlement. I have now asked for a refund of a year worth monthly debits and they are giving me a runaround and do not want to pay me.

Please refund me, how could you take premiums for a full year when I do not have any overdraft facility?