They refuse to return money after selling a broken car

A family member travelled to Cape Town and purchased a car from Mac's Auto Auctions on the 2nd of December this year. As we left the property with the car, the car had stuck without petrol. We bought petrol and started the car and the car then made funny noises and broke down just there and then( across the road from Macs auto auction). We went back and explained what happened and felt we wanted the money back. Debbie (salesperson) said that the money ( which was paid in cash) had already been deposited into the account and since my family are not from Cape Town and had to travel back home, they would deposit the money on the Monday (This being the Saturday). She wrote a note in her own handwriting and signed it. The car was left at their premises (they have the car and the money). When they were called the following week to ask when the transaction will take place, the manager said that they cannot return the money until they have sold the car. The owner of the place also said that they could have fixed the car but if we seek legal advice they will not. They then called about a week ago to say that the car is fixed we can come and get the car and we again stressed the fact that we do not want the car we want the money back. We were then told that if they manage to sell the car, they will take 50% of they money as they sold it on our behalf. It has been 20 days and they refuse to return they money and they still have the car. We are utterly disgusted and devastated as it took a long time to save up the money that they simply just refuse to Return.