caller: is this <my name>?
me: yes
caller: do u have Rob's number? Im trying to get hold of him
me: I dont know a rob
caller: sure you do...ROB.
me: No I don't. I think you have the wrong <my name>
caller: No this is <my first and last name> at <my address>, right?
me: i dont know any rob. Where did u get that information?
caller: From some website.
me: What website:
caller: some website listing.
me: what website listing?
caller: Rob is at <some house number nearby>
me: I DONT KNOW HIM!
caller: well its real important I get hold of him. can i give you my number and if you see him you can get him to call me. It's urgent.
me: I have ur number, it came up on caller ID.
caller: Ok thx.

So from reading these other posts, this is definitely a collection agency.