Deposit on Private Sale of Car

im sell a car and I have accepted a deposit of 700 dollars in June 2017 on the receipt it say balance is due August 4 2017 it is now February 2018 and I have not recived any more money so I sold the car is the person who gave me the deposit get his deposit back . I say no he made a deal broke the deal now 6 months later he wants money back do I by law have to give to him
I live in Rhode Island
Thanks Domenick

Deposit on Private Sale of Car