I need help activating my AT&T voicemail

Before leaving for Alaska, I switched from verizon (Same SM-G900V phone) to AT&T. Now im in dutch harbor (I think AT&T service is provided by TelAlaska here?) and trying to activate my voicemail with no luck. I've tried dialing various configurations (+1, 1, 11, with my number) as well as turning off phone and calling it from another line (it will ring a few times, then hang up). I do have an internet connection. What can I do? I need voicemail.