My understanding is:
The $50 rebate is a reduction of the FESL owed by the pensioner. So if they have paid in full and apply for a pensioner concession with an effective date of say 01/08/2017 they would be eligible for a Statutory rates rebate of $187.50 and a FESL pensioner discount of $37.50. You would apply this to the rate account it goes into credit and you refund to the ratepayer $225.00. At the same time your reconciliation file that you send to OSR would let them know that you have applied a discount to that ratepayers account meaning they (OSR) would receive an amount less $37.50 for that period due to you granting a rebate against the FESL.