Hi neilyoung1,
Thanks for coming back to me on this one.
It looks as though you may need to re-add the Voicemail on to the phone number you are diverting the calls too.
Can you please click here and go through the diagnostics to add this back on?
If this doesn't work, can you let me know if when calling the mobile number directly, if there is no answer do you get sent to Voicemail then or not?
Pop back and let us know.
Thanks,