Hi GEORGE ROSS, I understand how frustrating this must be losing access to critical files and emails because of a partner thats no longer in business can feel like youre stuck with no options.
To regain access remove the old partner in the Microsoft 365 Admin Center set up billing with a new partner or switch to direct billing contact Microsoft Support to clear the overdue status and then update your payment method to settle the balance.
Do you already have access to the Microsoft 365 Admin Center or is the account completely locked at the sign in stage?
Best regards
Lucky Charm