bill collector trying to collect from someone who used to have my cell number

number shows up on my cell. i never answer unless i know the number or the name calling me. of course they didn't leave message, so it's not important to me.

stop answering your phone to everyone who calls and they will get the message.

I got a call from this number and I answered but when I said "Hello" they stayed silent - I called the number back and it was a automated line for a bill collector