How do I set up my voice mail?

I was on the phone with my cell phone carrier and was told to contact Apple support. My voicemail will not let anyone leave a message. The voicemail used to work fine. Can anyone help me with that? Thanks.

Voice Mail (Visual or Normal) all are Carrier Specific features. Contact your Carrier (Cellular Service Provider), the agency that issued the SIM / eSIM to you.

I was told to contact Apple support because they could not help me. I was on the phone for hours with my carrier.