iPhone incoming calls goes to voicemail when I am on FaceTime calls

While I’m on a FaceTime call, all my incoming calls immediately get sent to voicemail. No one is blocked, call forwarding is off, do not disturb is off. It used to ring so I could answer incoming calls if necessary but it no longer does this. I tried looking through my settings to allow incoming calls if there was an option but I couldn’t find one. How do I fix this issue?

[Re-Titled by Moderator]

Original Title: On FaceTime, Calls auto send to voicemail