He called me, asked if I was there, then hung up.

Didn't recognize it so I didn't answer. A blank voicemail was left. Tried returning the call while blocking my number and got a "fast busy signal" like the number is not working or not receiving calls. (The last time I remember getting a fast busy was while trying to call a pay phone; they're generally not able to receive incoming calls either.) So I still have no idea who called me from a Los Angeles number.

Same happened to me

I got a phone call on my Iphone by the number of 213-839-4723 which says that is a Los Angeles ,CA number but I try to call back but it just starts randomly beeping with some muffled talking in the background

Didn't recognize it so I didn't answer. A blank voicemail was left. Tried returning the call while blocking my number and got a "fast busy signal" like the number is not working or not receiving calls. (The last time I remember getting a fast busy was while trying to call a pay phone; they're generally not able to receive incoming calls either.) So I still have no idea who called me from a Los Angeles number.