Yellow Letter - Missed Phone Call - No Caller ID - Suggestions???

[Brendan Harrison]

Anyone have success tracking down an unknown number?? Sent about 75 targeted yellow letters after driving for dollars. Received a call AND a voicemail to our Google Voice account. The number came up as Unknown, and the person said they didn't want to leave their number, but was curious how much we would pay in cash. Any recommendations on how to proceed? Our ideas are: 1) Mail everyone again and say "sorry we missed you call, please feel free to call back if you are still interested." K 2)