Bro, they will find out one. The admin will realise the overpayment.
I suggest not using it and return it when the finance department realise the mistake during their audit checks.
If you can't pay? Instalment to return to the government.
Call the NS Hotline, tell them you are likely to be overpaid and transfer the case to the Finance department (NOT Defence Finance Organisation (DFO)!!! - this is another dept), correct department should be Salary Services Centre.