I've had this problem for about a year now and could never get it fixed. Usually people know that they can just text me if I don't pick up, but whenever I get an important call from school or work, it's frustrating that they can't leave me a voicemail and that it seems like I don't have a working phone/ reliable contact. I have tried everything. I have tried calling customer service, I have done so many keypad codes that I've found online.
When I press all of the codes, the call either fails if it's a long one, or it says the number is not recognized/valid/etc. I have tried: 222 / 212 / 789 / 03456000789 / **61*+44004mobilenumber# (with and without the first zero in my mobile number) / *#67# / *61*212**30# / and a bunch of iphone codes that I can't find under my "recents" tab on my iphone. I'm not able to connect to any of these. Nothing goes through.