Voicemail unavailable unable to authorize access

After reactivating my data plan, I attempted to set up my voicemail. I followed the appropriate steps; however, when I attempt to save my greeting, I get the message: "Voicemail unavailable- unable to authorize access."

I checked my network connection, Wi-fi and airplane mode are off; I reset all network settings before I called my provider (Verizon). Provider said nothing is blocking my access. Rep has no clue how to assist me.

What do I do now?