Voicemail not working

Voicemail not working on new iPhone SE 2020.  Recently switched from an Android with Verizon to Xfinity Mobile.  Visited Xfinity store, they could not solve problem. Chatted online with Apple, they could not solve problem. Went to Apple Store, they could not solve problem.  

Please help solve this problem.  Getting frustrated after hours of talking to Techs who can't solve this problem.