Startups: Companies that are in their initial stages of business and typically developing a business model and seeking financing.
I think the billing account needs a separate look from the closed subscription. Historical charges can include deleted resources. If Cost Management + Billing → Invoices still shows the invoice, the usage CSV can help trace charges by date, meter and resource ID. If it's inaccessible, check the original sign-in, directory and billing permissions. Since Billing Support keeps sending u in circles, Microsoft for Startups Program Support is another route. It's under Get program support on the Startups homepage.
In that private ticket, include the closed subscription ID, invoice dates and amounts, when u reduced usage, and where the support process gets stuck. Request the detailed usage breakdown and a billing review for a possible goodwill credit.