It's probably cause you're att email. It's Verizon ma'am. Jk.
Yeah if you updated your phone, it's been having allot of issues with voicemail.. Battery life, ram & lag, even things like predictive text through swype.. Yeah it's been garbage. I am sorry about the issue. I believe one of tech articles I read brought up some solutions. My issues weren't really resolved though. But it's worth a shot.