iPhone 8 voicemail

On my iPhone 8 that my daughter gave to me when she upgraded, I am having trouble figuring out how to set up voicemail. I hit a roadblock when asked for a three digit code, which to our knowledge was never chosen or assigned. When initially setting up the phone for myself, I chose a password. Also, rather than trying to set up using Apple, should I go through TracFone (my monthly provider of my talk, text and data)? Thanks for any help offered!