Hello everyone!

I am having an issue regarding my phone system, specifically dealing with a single extension.

On the problematic extension, all calls made from outside the system goes straight to voicemail. I have made sure to check Do not disturb, which was not activated. All Call forwarding is disabled with the exception of Busy/No answer which goes to the voicemail box. I have tried everything I can think of, and I am wondering if somewhere along the way there is a setting I accidentally changed, but I just can't find it. What do I need to do in this situation?