Reverse Urgently

I made an EFT payment to pay my monthly payment. As the account, the debit order was going off, was closing. I had to pay overdraft on the account. So that i can finally get the account closed. NOW the money has been deducted today. After I have already paid for it. This money was not there for you to take. I was told to call FNB to reverse the payment, they have advised that it is blocked. U need to unblock or reverse on ur side. Now ive been told this cant be done. I need the money back in my FNB account...R842.34 ASAP. So that i can close my FNB account.