Called and left no message

The caller did not leave a message and called more than once.

Called and a message was left by accident. Sounded like a man and woman having a casual conversation in background but could not make out the conversation. Maybe two people in a call center? Not sure

Called 2 consecutive days, didn't leave a message

Received several calls from this number of the past week. Never leaves a message (generally I don't answer calls unless the number is in my VIP list). I'll be blocking it.