Has anyone else noticed lack of notification when voicemail is being left?

We've just discovered a whole bunch of messages dating back to April this year; but as far as both my wife and I are aware, the old "notification" icon our DECT phone used to display (on the OLD Orcon backend) wasn't displaying, and we've not heard the "interrupted dialtone" either.

(Issue raised with Helpdesk)

Edit: Clarify subject line