Extension available always goes to VM but

[Windows LiveUser1]

Hi,
I have a strange thing happening.
I had an extension XXX working hassle free. Cisco phone is connected to it
a few days back it stopped ringing and XXX dialed it goes directly to the VM

I have checked that phone is not set to DND. can still make calls from it.
from the server activity log it tells me that it is forwarded to VM due to busy or unavailable.
I have tried to use 3cx softphone and have the same issue.
I can delete and re-create extension but really would love to know where it could be fixed instead of re-creating.
Thanks very much

 

[mixig]

Same behavior with internal and external calls? office hours/outside office hours, exceptions in extension settings?

 

[leejor]

Is that the only appearance of that extension, and is 3CX set to NOT allow more than one call (to that extension number)?

 

[ian.watts]

I may be asking the obvious.. but is the extension's status set to Available? It won't ring without that.