Seller hasn't paid in 3 months. And Won't Respond to Letters.

[Joey Bricio]

I sold a property "owner finance" at the end of last year. We signed a contract for deed stating that after 3 late payments the contract shall constitute as a default. This month will be the 3rd month he hasn't paid and the 4th time he is late. Obviously I know that the economy and covid-19 is a big reason for his troubles and lack of payment. 

Ive sent letters in the mail stating that I'm willing to set up a payment plan to help the guy out, but i haven't got a response back. Don't know what I should do, or if there is anything i can do. Any advice ?