Samsung — Coupon provided for damaged product has time validity

I have purchased Samsung washing machine which had dent on arrival for which i did request for replacement.
But they mentioned that product does not have replacement option.
So provided me2 options:
1. Get the coupon as goodwill gesture
2. Return the product n get the full refund.

as i don't wanted to go for return and start again fresh order process.

I opted for coupon which thy provided me but with a one month validity which is not acceptable to me as i don't have anything to buy in one month.. so it will get void after it.

I have requested for coupon validity by atleast 6 months for which i am not getting meaningful response.