Seller lawyer contacted me, seller wanted property back! HELP!!!

[Jimmy Ho]

Hi everyone,

I've purchased a vacant land from a retired lady. I purchased the property a while back roughly 6 months ago for a fair price. The seller lawyer had sent me (2) letters claiming that I took the property wrongfully, and the property was worth a lot more than what I had purchased the property for. 

1st Letter: 

Stating that "...the seller did not fully understand the transaction, and it was not her intention to transfer title..." and since she couldn't drive; I drove 100 miles to go to her place and pick her up, so she can go to a notary place to sign the grant deed. The lawyer also accused me for "...pursue your very unprofessional, illicit and bad faith conduct in obtaining title." The lawyer claiming the seller wanted the property back and she will pay the full amount that I have paid for, along with the delinquent tax that I had paid. If I don't ...they will take it to court.

2nd Letter: The lawyer told me that they had obtained the appraised value of the property at the time of purchased. The seller want the full amount of the purchased price to be the appraised value or else they are going to file court action. The lawyer also wants me to give him the purchased agreement that the seller had signed additionally with the grant deed (I do have that agreement in-which both parties had signed and had gave the seller a copy already at the time.) He wanted to see the purchased agreement and I refused to give it to him. He stated "I do not understand your reluctance to do that, if such an agreement exists". Stating that they will request a judgement against me not only the value of the property, but also for HER ATTORNEYS FEES.

Questions:

1. What should I do? I'm the owner for the property.

2. Do I have to response to his letter?

3. Do I have to provide anything that their attorney ask for?

4. What rights do they have?

5. What rights do I have?

Thanks, 

Jimmy

P.S: Sorry for the lengthy information.