unauthorized debit order

After numerous complains about Nedbank passing the un authorized debit orders to my cheque account the have not stopped double debiting my account even though we came to agreement of paying the normal installment and then made an agreement to pay r320.00 towards my arrears . .I reported and complained in 28 May 2015 and was refunded ,again on 5/10/2015 was also refunded .They have done it again and i am still left dry .On 3/11/2015 R637.69 debited by Nedbank , just need the amount refunded back because it has left me with nothing again.