Rrb — refund o[censored]nsuccessful transaction

I, sanni kumar sinha, had applied for rrb alp & technician this year on 4th march, 2018 and made payment from my idbi bank rupay card.

While making payment first transaction was unsuccessful and hence i made payment again of amount rs.500.in this way payment of rs.1000 credited to rrb instead of rs.500.
I approached my bani idbi for refund but they did not refund stating that merchant (In this case rrb) did not agree to refund.
Rrb has declined refund stating that payment once made cannot be refunded but in my case payment has been made twice and i amm asking for refund of only 1 and not both.

Attached the denied message from rrb.

Rrb registration no.[protected]
Contact no. [protected]