Chris Hannan Greetings & Welcome to Microsoft Q&A forum!
I can't seem to find a way to reach support to challenge the cost.
You must have the appropriate access to a subscription in order to create a support request for it. This means you must have the Owner, Contributor, or Support Request Contributor role, or a custom role with Microsoft.Support/*, at the subscription level.
If you have the required role permissions, you can create free billing support ticket to know more details about your cost and charges. create a support request.
Also, see Cost Management + Billing frequently asked questions (FAQ) for more details.
Do let me know if you have any further queries.