made a purchase by mistake

If the purchase was made directly from Microsoft, the fastest self-service path is to check the subscription or order in the Microsoft account used for the purchase.

1. Go to https://account.microsoft.com/services.
2. Sign in with the Microsoft account that made the purchase.
3. Under Services & subscriptions, find the product.
4. Select Manage.
5. If available, select Cancel subscription and follow the prompts. During cancellation, Microsoft indicates whether the purchase qualifies for a refund.

If the charge is unexpected or it is unclear which Microsoft account was used:

1. Go to the Manage your payments page and select Investigate.
2. Review whether the charge was caused by recurring billing, a family member purchase, a previously declined charge being retried, a preorder or split order shipping, or an in-app purchase.

If the purchase was an app or game from Microsoft Store, a refund request may be available through Microsoft Store refund options.

References:

• How to investigate a billing charge from Microsoft
• how to get a refund for365 - Microsoft Q&A
• What has been purchased? - Microsoft Q&A
• Get a refund for apps and games purchased from Microsoft Store