Talkswitch memory usage

I have a TalkSwitch 48 CVA unit with 30 minutes of voicemail memory.   98% is apparently used up, yet, for this unit, I have cleared all voicemail messages. There are (apparently) none on the system, andonly two pre-recorded greetings of 18 seconds total. So, how to I find/clear this memory?  This is preventing callers from leaving messages.

Thanks!

(and yes, I'll be upgrading to new equipment soon!)