Not receiving voicemail

[markhsw1]

On two Nokia Lumia 520 Windows Phones on two separate lines, voicemail sometimes shows up one to two weeks after the message was sent. This has resulted in missing notification of the death of a dear relative, and problems with MD appointments. One of the phones is on 8.1 the other is on 8.0. AT&T is the carrier. So far they have been no help.