You have to be as accurate as possible when entering credit or debit card information. You must enter everything as printed on card/what your financial institution has on file, such as account name holder, address, your 3 digit code, ETC.
If you've changed any of your personal information with your financial institution recently, this can also have an affect on why your card is being declined. Sometimes, even the slightest change, such as adding a new phone number can affect how you use your card for online purchases.
And if you really wish you bought an Xbox, don't think for a moment you'd have it any easier if you're the one doing something wrong. This can happen with any method of online shopping with any gaming system, phone, digital device, or PC. Xbox isn't exempt.
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