Google caller ID Spoof. Some collectors use this. They might spoof a number on your cell phone from home, etc. in order to get to you.
Buy a caller ID spoof, they are rather in expensive cards online. Call up the collector and make it appear that you are calling from withing the same office. LOL. Remember you are always dealing with what is not much more than high school students here. Tell them you'd like to come round and talk it over personally.