Hello! My name is Ben a fellow member here in the community, not a Microsoft employee. Hope you are doing well!
You can actually do a split payment using your Microsoft balance or gift card. Then pay the rest using your credit/debit card. Once you redeem the Microsoft balance or gift card to your account, you can select it to buy the game you want to buy and if the balance is not enough. You will then be asked on how you would like to pay the rest, you can choose your credit/debit card this time to settle the rest of the balance.
This thread on one of the community forum might help on how to do this:
https://answers.microsoft.com/en-us/xbox/forum/....
I hope the information helps somehow. Feel free to post back in the community if you have other questions and we fellow members will try our best to help.
Best,
Ben