NEDBANK MFC DOUBLE DEDUCTIONS REFUSING REFUND

I have a vehicle loan and I was unemployed for so long, last month I started working but my salary was delayed and my due date for the car installment was the 7th of each month. I got paid on the 11th so I made an EFT for the car, however the bank went a d deducted my account for the installment two days later so I paid double in one month. I called many times asking for refund so I can pay my other debts they kept saying in 7 to 10 days., I never received the money. So now this September they say I am behind with installment and I tell them allocate the money that u deducted post the due date and allocate it to this month, it looks am not getting anywhere cause each and every day am getting the call from different agents of NEDBANK MFC to make a payment, meanwhile they are the ones who double deducted and refused to refund me