Who called from 8183342572

Calls several times per day, no one there. Call back is non working number

818-334-2572 calls several times a day. No voice msg.

Getting calls regularly once a day. Don't know anything about it.

Calls office number every few days, nobody says a word, hangs up.

Have you considered blocking this incoming number?  You might want to contact your provider to find out if that is an option.  If your office is small enough, maybe you can just tell the other employees not to answer.