Unknown number calls not coming though, even though “silence unknown Callers” is turned off

I’ve had a few instances recently were people have tried to call me from a number that is not in my contacts, and they are sent straight to voicemail. I don’t get a missed call notification, it’s not in my recent call log and it doesn’t even ring. The only reason I know they’ve called is because I either have a new voicemail, or they tell me in person they have been trying to reach me. “Silence unknown callers” is toggled off, and Do Not Disturb is not on. I do get some unknown numbers ringing through, but I know some are not! It’s very odd and any help would be appreciated. It’s been a nightmare recently as I’ve missed some very important calls!