Multiple users of the same outlook email address

I have a issue where someone has been able to register the same outlook email address as me. I would to stop receiving their emails and would also like clarification on whether my email is secure. At the same time I also started to receive some other emails also from another person with the same email address as me. This has been happening since Saturday.

I have had one email conversation and they said they were trying to migrate from hotmail to outlook and had picked the same email address as me. They didn't see any messages telling them the email address was already in use. Can anyone help?

Thanks

Sandra