Horrible service not treating customers fairly

My wife and I were selling a car and we advised on this website, 2 days later a gentleman named Matthew came and did a review on the vehicle and he told me he can giv me 20 thousand for the car, he left 3k for me to go renew the disc and I signed a document to say I have the R3000 deposit on me, he took the car docs with him that il giv him the car wen he pays the remaining balance. To cut it short I have changed my mind on selling the car so I called Matthew to give me an acc where I can send him his 3k nd he return my docs my he ignores my calls and texts ? Whr is the cancelling clause in all this ? Why is webuycars treating people like trash ? What kind of employees do u have ? I just want my papers as I don’t want to continue selling my car ! My car is still in my position