I refunded a game but the 10$ of discount applied for the first buy with pro is not available again
Sorry, but it was stated in the terms. And in not so small letters that the voucher is not refundable.
If you think it’s a unique situation or a mistake you should contact the official support channels.
Indeed, if you ask a refund for a game where you used the discount, you'll lose the voucher because it is used.