Just cos you changed provider does not mean your old email accounts get cancelled. The providers quite often leave them open.
You need to change your email address on all the important sites that you are registered with, make sure everyone important knows your new email address, then delete the old account in Outlook Express.
My father in law couldn't work out why he kept getting messages to his old account from some shopping site. I said 'have you told them your new address ?' ........... 'err no'.