If you didn't set up a new password it would be the last four digits of your cell number. Otherwise call customer service and then will ask a few questions to make sure you are the owner of that cell and reset it for you. 800-922-0204 or you can try this
*228 option 1 will only try to activate a phone if it is not currently activated. If you just dial the *228 choose option 1, it will "reprogram" the phone and set the security and lock code to the last 4 of your phone number.
You can try the last four digits of your mobile number if you have not set up a password. Customer Service CANNOT reset that password for you. We do not have remote access to your personal information on your phone including passwords. I don't see why type of phone you have. The best thing to do would be a master reset. Search our support page for "Master reset" for your device type.
Have a great day!