Debit order returned after funds transferred into account

Debit order returned at a cost of R120 after funds had been transferred into the account to cover the debit order cost. I transferred the amount required to cover the debit order via online banking. My debit order was returned at a cost of R120 which FNB refuse to refund despite acknowledgement that the transfer was pending. The transfer was made from another FNB account using the online FNB application and as such should have been immediate. Even my account statement shows the debit order running, then the credit for the amount and then the returned debit order. I want the cost of this refunded into my account.