Are you a VM broadband customer? Is the email address linked to your biling account (look on the my profile page scroll down to my services, or on the manage accounts tab for secondary addresses).
If yes to both the most likely reason is that the address is locked for security reasons. You should change the password for the address and wait here for the Forum Team (VM employees). They will get your personal details by private message to pass security and then check the status in the system and see what is wrong - and unlock it if my assumption is correct. They can take a day or two to reach this thread, but it is worth the wait rather than risk the telephone customer service route.