Direct calling on extension not working

Hi, 
I have a user who's direct calling on his extension is not working. From what I Can find all other users' are working fine. It's only his. I compared his profile to another user's and cannot find any differences at all. for example let say his company number is +41 245 154 000 and his extension is 314. Essentially if you phone +41 245 154 314 it needs to ring with him. The extension is configured correctly and when you phone the number it rings but doesn't seem to ring with anyone. I checked the related posts but didn't see anything like this. 

Thanks.