Call 1-800-513-5015 Monday-Friday 8:00am to midnight. They should be able to help you.
You're probably on Fidelity's mailing list. You can always write RTS and put back in your mailbox to have the mail sent back to them, but an easier solution might be to give them a call when you have some time and can multitask when you are sitting on hold listening to elevator hold music which is designed to burn your brain cells out. Here's their contact info: http://www.fidelity.com/inside-fidelity/contact-us/contact
If you are still getting literature from Fidelity, there's a good chance that you are still "on their radar" so to speak. I'd suggest calling the Human Resources Department at your former employer for more information. If you have money in the plan, you should be receiving a statement at least annually.