If a person has received a payment of a pension or other benefit under these regulations or the former regulations and it is subsequently discovered that, owing to a miscalculation or to a mistake of fact for which the person is not responsible, the payment was in excess of the amount properly payable –

(a) the Board may require repayment to be made on any terms that the Board thinks just; or

(b) the Board may write off the whole or any part of the excess amount so paid if it is satisfied that enforcement of the repayment by that person of the excess amount would impose on him or her undue financial hardship or would be inequitable.