Insulting Letter

I received an insulting, disgusting, and infurating letter today from a land developer in Arizona. They were offering to buy my property. But they were only wanting to pay $4000.00. Now mind you we paid almost $200,000 for our land, and house and that was three years ago. Since then we have fenced it, and added a hay barn, horse shelters and pens and a small shed for wood and tools.
On top of this insult when I tryed to call them they refused to talk to me.
I am still upset and mad about their letter and offer.