How to Redeem:
Go to the Microsoft Store Xbox website at https://www.xbox.com/en-US/microsoft-store. Sign in to your account.
Go to the 'Games' menu and choose 'Redeem code'.
Enter your 25-digit code and click 'Next'.
Once the code is verified, you will see the confirmation message. Then you will be able to download it on your console.
How to check your balance:
On Xbox, you can check your Microsoft account balance on your Xbox One console without going online.
Select System > Settings > Account > Payment & billing. To help protect your account, you may be asked to enter your password.
You’ll see Payment options, where your balance is shown under Microsoft account. If you have several payment options, you may have to scroll right to see it.
Your current gift card account balance will be displayed.
Abridged terms and conditions:
There are no fees or expiration dates.
Many digital codes from different publishers look similar, and some Xbox games include codes meant to be used at the game publisher’s website instead of through Xbox. Make sure that the code you’re trying to redeem is supported by Xbox.
You need to be signed in to the Microsoft account for the person who is trying to use the code. If the code was purchased through a different account (for instance, as a gift), be sure to sign in using the account for the person redeeming the code (the one that received the gift).
Some codes can’t be redeemed if your Microsoft account is suspended or has a balance due. Resolve all account suspensions and unpaid balances by going to the Services & subscription section of your account before redeeming the code.
You can only use some digital codes in specific regions. Confirm that your account region matches the region where you purchased the digital code.
Phone and Chat Support: https://support.xbox.com/en-US/contact-us