Dear Nigel,
That sounds frustrating, especially after being routed somewhere you cannot even sign in to. Unfortunately, as a forum moderator, I am not able to look up payment records or trace a charge to an account for you. My role here is limited to general guidance you can apply from your side.
First, check the invoice or reference number on the charge. If it begins with G or E, the charge belongs to a commercial subscription rather than a personal one. In that case your IT provider is the right contact, as they hold the admin access and can raise a service request with Microsoft billing on your behalf. For detailed instructions on how to get support, please refer to Get support - Microsoft 365 admin.
If it is not a commercial invoice, start with the Investigate tool, as it works from the card rather than the account.

Sign in to your Microsoft account dashboard, open the Manage your payments page, and select Investigate next to the charge you do not recognize. There is also a troubleshooter on the same article that walks through the most common causes, such as a subscription with recurring billing still enabled, a family member using your card, a previously declined charge being retried, or an in app purchase.
For reference: How to investigate a billing charge from Microsoft | Microsoft Support
If that does not identify it, you can reach consumer billing support directly:
- Go to Contact Us - Microsoft Support in a browser.
- Choose Microsoft 365 > Get Home support.
- Describe the issue in the box under "We're here to help", then select Get Help.
- Scroll down and select Contact Support, then sign in with your personal Microsoft account.
- Under Products & Services choose Microsoft 365 and Office, then select Billing as the category and confirm.
- Choose the chat option to reach a support specialist.
Finally, if you suspect your card details have been used without your permission, contact your bank directly to block further charges rather than only disputing this one.
I truly hope you get your issue resolved swiftly. Please know that even though I can't directly intervene, directing you to the correct, specialized support is the most effective help I can provide from my position. Thank you for your patience and understanding. Please let me know if you need anything else. Wishing you all the best.
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