Changing billing option

Try managing it from
www.commerce.microsoft.com. Click on payment options and add the new card, but I think it should already be there since you said you added it. (But, confirm it is listed on the left hand side just to be sure.) Then click on subscriptions. Right above
your gold subscription you should see the option to "manage". Click on "manage" and a popup will come up that allows you to "change payment option" . Select next and proceed to switch the payment option over by selecting the credit card you just added.

If the site will not allow you to switch the card it could mean there is a large billing issue and you need to contact Xbox LIVE Support at 1-800-4MY-XBOX if you are in the US or Canada or go to
www.support.xbox.com/contact-us to get contact information if you live elsewhere.

This is unbelievably complicated and difficult. I have attempted to speak to somebody online but the chat doesn't work. It really shouldn't be this awkward to change a payment option.

https://support.xbox.com/en-CA/my-account/microsoft-account/update-microsoft-account-country-region

You must follow the instructions on this site

Should be noted selecting a region that isnt your own isn't suggested

So if you are selecting the us for English content and using us prepaid cards that won't work for.all.games

As.some.are.region locked

https://support.xbox.com/en-CA/my-account/microsoft-account/update-microsoft-account-country-region

You must follow the instructions on this site

Should be noted selecting a region that isnt your own isn't suggested

So if you are selecting the us for English content and using us prepaid cards that won't work for.all.games

As.some.are.region locked

Thanks for yor reaction,

I've read the page you suggested and tried this. But my problem is that in some strange way my billing information that is filled in in my microsoft account is not connected to my xbox as I need to fill in new billing options when I wan't to dowload a game..
And at this point my xbox thinks i'm registerd in the US so as I can't make an dutch adres... And a dutch adres is on my credit card so I get the message there is a region problem. Or do I oversee something?

You cannot move already redeemed currency to another xbox profile. However if you want to use the currency on his account you need to make some changes.

Sign into the adult account associated with the child account on Xbox.com. Go to "Security, family, and forums". Then go to "Online safety for Xbox One" (I know you stated 360, however the option for enabling purchasing is under the Xbox One section.) It
will ask you to verify your identity. Go ahead and send yourself a verification code by whatever means it asks you. Once your in, select his profile (it will give you your profile and his profile to choose from). Allow him to make purchases through his account.
Save the changes. (and use that currency)

If you have no idea what the parent account to your son's account is, call support. They will be able to help you out with figuring out what it is.

Hope this helps.