27-10-2013 07:34 - edited 27-10-2013 07:37
Turn the O2 voicemail feature off by dialling 1760, and then ask someone to ring you again to see if the issue resolves.
Their has been threads on here recently about voicemail issues.
Dial 1750 to turn it back on.
Look in this recent thread.
on 27-10-2013 10:35