You will need to reinitialize the vmail. That is the only way to have the vmail recognize the 3 digits. While the vmail is connected to your phone system, do a Feature 983, log in as usual. When it comes up dial 1 on your dial pad. It will ask you for a password, type in REINSTALL. Reset Database? Yes.
Give it a good 5 minutes to default everything out. Even if it goes back to date and time. Give a few minutes. Then do a Feature 983 and it will come up password instead of log. Put in 266344, it will ask a series of questions, I usually just say yes or okay or next to everything that comes up. It will configure itself then you will be able to do a Feature 983 and log in using 1002 0000.