To redeem, enter the Minecraft Minecoins code on https://www.minecraft.net/redeem/minecoins.
Great news, your Minecraft Minecoins code does not expire.
To redeem your code, you need a Microsoft account, create one here: https://account.mojang.com/.
You can contact the Minecraft customer service here https://help.minecraft.net/hc/en-us.
By using this service, you consent to the terms and conditions of Minecraft Minecoins . To view these, please visit https://www.minecraft.net/terms