How do I contact this landowner?!

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I'm having a tough time here..

Basically here's what happened:
- Found a very nice lot for a decent price that looks like it's been for sale for a 2 or 3 years.
- I write down the phone number that they have on the for-sale-by-owner sign.
- I call the number, the guy has no idea what I'm talking about.
- I drive back (waste 60 miles of gas) to make sure I wrote it down right. Turns out I did write it down correctly.
- Contact the county accessors office, they give me the address of the owner (which is the same name/address I got when I did a reverse phone number search on the number on the sign.)
- I am now writing a letter to the people whose address is what the county gave me which is the same address that turned up on the reverse phone number search which is the same phone number that the guy had no idea I was talking about.

Does that make sense?
What happens if they never respond to my letter, or the people with the sign moved?

:/

I REALLY want this land but what the heck - you can't get ahold of the gosh darned land owners.