i can't set up my voicemail???

so i had an old 6s that i set up my old voicemail on, idk what ios version it was on but i hadn't updated it in a while bc i was out of storage... fast forward a few months after i stopped updating, my phone battery completely died (unrelated to the lack of updates i presume). so i got a new/refurbished 6s, and it's not letting me set a voicemail password?? on my old phone i didn't even have to do that, so it's weird to me. now i can't even call voicemail to set it up, or receive any voicemails even though when i asked my friend to call me to see what my voicemail message sounded like she said it was the same one as my old phone, so idk what the deal is or why it keeps saying "voicemail unavailable" whenever i try to set a password. :/