Owner refuses to take vehicle back

My name is Musa Magagula I bought a vehicle in Pretoria at Zambezi a Toyota Yaris at Bezcor Auto car dealer for R65 000 cash on their business card it says they sell quality secondhand cars on purchasing the vehicle they informed me of one defect which was the windscreen of the vehicle and assured me that it was the only defect of the vehicle. After a few days travelling with the vehicle I noticed some things that gave me concern on the 2 of June 2015 I then decided to take it to a mechanic for inspection only to find that the vehicle has a damaged valve in the engine and the shock absober on the right front wheel is also damaged in which repairs would be costly. I contacted the car dealer to inform Him with this discovery and He told me He cannot help me with this problem and so I asked Him if I can bring the car back for the cash I bought it for and He refused to take it back and told me that I have signed the contract and there is nothing He can help me with. I would like to plead with you to please help me to settle this matter. Thank you.