Hello @Peter Kirkpatrick
Firstly, I would suggest checking your billing history to see if there are any active subscriptions that you may have missed. You can do this by logging into the Azure portal and navigating to the "Cost Management + Billing" section.
From there, you can view your billing history and see if there are any active subscriptions that you may have missed cancelling. If you have already cancelled all your subscriptions and are still being billed, you can try contacting Azure support directly. You can create a support request by following the steps outlined in this document: https://docs.microsoft.com/en-us/azure/azure-supportability/how-to-create-azure-support-request
If you are still having trouble creating a support request, you can try posting your issue on the Azure forums (https://docs.microsoft.com/en-us/answers/topics/azure.html).
I hope this helps.