how about learning the hard way

Aha.., yes..., of course... But you realize, you have dialed the wrong number?

situation: I call people for free (flatrate). (Of course) the call gets canceled by phone company after 2h. The other person calls me now back. I wait for the ring to stop. 1 min now and still ringing. Hm, I get a little restless. Please, hang up!
Hard decision, but I take the call Some just learn the hard way (wonder what the face looks like when seeing the bills). Now the best: I ask "Why did you not stop after the first ring?" and response: "Oh, oh, did I call you? Shit"