After the voicemail message is broadcast the call is dropped immediately, with the result that I receive an "empty" message (via email).
I just quickly changed your voicemail to email to my email address and I added your registration to my phone and did a test call that I let go to voicemail. ( I have changed everything back again.) It worked and it let me leave a voice message and it sent me the audio clip. See screenshot below
Re-tested and now found to be working.