Bizarre - calling wrong number

My mother (on google phone) tried calling my son (on iPhone). He missed the call. She left a message. His phone shows missed call but no voicemail. However, his *best friend* who is not a contact of hers gets a missed call and her voicemail. He texts it to my son. Weird right? Then I call my son to see what happens. Phone rings, we let it go to VM. Friend also get call, and my call goes to the friend’s VM?!? He’s not a contact if mine either. He’s miles away. What is happening?!?