Can someone hack your account by giving them a Microsoft refund request denied code?

With what you're telling us here, I would suggest you contact your bank, and file a police report for the theft and credit card fraud.

Also, if you got an email denying your refund requests you should be able to reply to it and request a review on the refund requests.

Recover Microsoft Account

https://support.microsoft.com/en-us/help/10494/microsoft-account-recover-hacked-compromised-account

This link will take you to Microsoft support on investigating fraudulent charges and what you can do about them.

https://support.microsoft.com/en-us/help/10623/microsoft-account-investigate-billing-charge

You can't bypass region locking. Your friend can request a refund or give the code to someone else.

There's no way around region locking. You can request a refund or give the code to someone who is in your region.

If you already put the codes into the account then I do not believe the retail store will give you a refund.

- can I get a refund if i put in the codes, don't use the gamepass and immediately request a refund?

No. Microsoft would not be able to refund them since they weren't purchased from them. So once they are added to the account they cannot be removed.

You're welcome. Your friend should be able to request a refund for it or he can give the code to someone else if needed.