why does facetime show a missed call notification on mac even though I never use it

Every time I open my mac notebook facetime shows that I've 4 notifications. I don't use facetime.

When I click the app it opens and asks me to sign in which I don't do as I don't use it. Then the notifications disappear only to reappear when I reboot my computer.

How can I stop this happening or how can I turn off notifications?

Thanks in advance.