I have been charged a $100 and i have no idea what for?

Use the Microsoft account billing tools to identify what the $100 charge is for.

1. Go to the Manage your payments page of the Microsoft account dashboard:
   • Sign in with the Microsoft account that might be associated with the charge.
   • Find the payment method that was charged and select Investigate next to the unrecognized charge. This tool walks through the most common reasons for unexpected charges and helps identify the product or subscription.
2. Check for common causes of unrecognized charges:
   • A Microsoft subscription (for example, Microsoft 365) with recurring billing enabled.
   • A purchase made by someone you know (family member) using the same card.
   • A previously declined charge that was processed later.
   • A pre-order or split order that has now been billed.
   • An in-app purchase from an app or game.
3. If the charge is related to a subscription that was believed to be canceled:
   • Go to Subscriptions at https://account.microsoft.com/services and check the subscription status and end date.
   • Charges can still occur if cancellation was done less than 2 days before the billing date, or if a different Microsoft account is actually being billed. If the wrong account was used, return to Manage your payments and use the Investigate flow to confirm which account is tied to the charge.
4. If the charge still cannot be identified or appears incorrect:
   • Use the troubleshooter linked from How to investigate a billing charge from Microsoft to further analyze the charge.
   • If needed, contact Microsoft Billing Support from the support site and provide details of the charge (date, amount, last 4 digits of card) so they can review the billing on the account.

If there is concern that the account or payment method has been compromised, also review recent purchases and subscriptions on all Microsoft accounts used with that card and consider contacting the bank or card issuer to secure the payment method.

References:

• How to investigate a billing charge from Microsoft
• Unable to cancel your Microsoft subscription
• Understand your invoice for your Microsoft MOSA billing account
• investigate a billing charge - Microsoft Q&A
• refund please - Microsoft Q&A