Why cant people leave me voicemails??

So for aome reason my phone updated and now I cant get voicemails. And i dont mean i cant check them i mean when my phone rings instead of going to voicemail it just hangs up on them. It doesn't go to voicemail. Why is this happening?? and how can I fix it?? I have a child who just started school, I have a job and I am currently in school myself so its very frustrating that no one can leave me voicemails if I am busy and cannot answer. It disrupts my whole flow.