"I logged in with the right username and password, but now it's asking me for a security code. I don't remember / have access to the email address linked to my account."
MxM employs security features that protect the website. One of them is called.
This means that MxM will prompt you for a 6-digit confirmation code if it doesn't recognize the device you're logging in from. Many, many websites do this. Please make sure you have constant access to the email you signed up with, or you will eventually face issues logging in. If you need to update the email address we have on file for you, email us your username and let us know what happened.