My iPhone 6 is not receiving voicemails?

I got my “new” iPhone 6 back in November (it was previously owned). And I noticed that I wasn’t receiving voicemails. People can call me and leave a message but the voicemails don’t make it to me. I also noticed if I tried to make a custom voicemail there would be an error so it’s stuck ar default. I can see and access my old voicemails from before I swapped phones however. I have no idea how to fix this and I wanted to ask here first before going to Apple for help.