Closing an account (as long as it is still active) should really not be that difficult. The problems occur if the account has been deactivated for any reason - then you need to get it reactivated before you can close it. When you say 'no longer operating under that name,' - did you change your business name at some point and not inform Amazon ? - and so Amazon are not recognising the new name ? Your fist step would be to open a case with Seller Support.