I don’t think that there is any chance for recovering deleted voice from ansaphone or digital answering machine. However, you can check and follow below mentioned solution:
1 – Check if your ansaphone has any USB flash drive connected. If there is any USB drive like memory card or something like that store the recorded voice then you can try Digital Media Recovery Tool.
2 - If there is no USB drive then you can contact the manufacturing company of ansaphone. Hope they could help you.