I was on the opposite end of this about 12 months ago. Got a call from a UK landline number so let it ring out then called back a bit later.
Some woman: Hello?
Me: Yes, hi, I had a missed call from you?
Her: I don't think so, not from me.
Me: Well, I've just pressed redial on the number that called me.
Her: Well I haven't made any calls.
Me: Oh.
Her: So who are you, then?
Me: Well, I don't really want to say since I don't know who you are.
Her: And in that case, I wouldn't tell you either.
Me: That's fair enough. Alright, bye then.