Voicemails not carrying over to new phone

My mom recently upgraded from iPhone 6s to iPhone 13 Pro. Everything carried over except her voicemails. She can access them from the old phone but they don't appear on the new phone. I left her a voicemail as a test and neither phone shows she has a new message. The person at the Verizon store told her they would carry over automatically but they have not. We are trying to make sure she doesn't lose any of her messages