I have a problem with a classic voysys unit that the administrators mailbox has been deleted by error, can you help me?

"I am at my wits end regarding this voice mail unit.

The Administrators mailbox had been deleted by mistake, therefore even when you reset by holding the diagnostic button for 12 seconds,resetting the password to 23646, there still is not an administrators mailbox.

I have tried each mailbox using the password 23646, 10-29 & 900-999, each time the reply is "you have entered an incorrect mailbox password combination, please try again"