Unfortunately you'll probably have to cut your losses on this one.
Depending on how the company is being wound up, even if you were able to get in contact with them, because you're technically an unsecured creditor of the business, you'd just have to join the back of the queue for any leftover money.
If they were to start trading again, you could see if they'd be willing to extend the expiry date for you - but they're not obliged to. You're at the mercy of their good will on this one.
As as happened in other cases, if they were to start trading as a different entity, you may find that the new entity will not honour any vouchers issues by the one that shut down.