Sounds ok to me But go to voice mail in main menu, not under users and devices,
Go to voice mail users, search for your extension,
If it exists then check that extension number and mail box number match.
Then go to call routing and make sure calls route to voice mail on no answer and busy.
Also make sure mail box has been set up, dial voicemail from extension, put in default pin code and follow instructions to activate mailbox.
To test it make extension busy then call it , call should route to mail and give correct anouncement.