Bad used cars and after sales

I bought a Chevrolet Vivant 1.6 from Rob Mackenzie at his Park and Sell dealership on the 28th December 2015. He advertised it as excellent original condition extreme fuel saver drives like a dream.<br> <br> It drove okay until the 4th January 2016, the vehicle lost a lot of power and became very jerky. I then called him and he said I should bring it in. So I took the vehicle to him on the 5th. His mechanic had a look at it and tested the spark plugs and said it is now fine to drive, but when I drove it around the dealership yard it was giving the same problem with no power and still very jerky.<br> <br> I then told Rob I am not satisfied with the vehicle and would like a refund or another car of the same value. He couldn't give neither and said he would fix the car and resolve the jerking and loss of power by the 8th EOB otherwise he would give another car of the same value or a refund. I asked him to put it in writing and sign it which he did.<br> <br> The 8th came and still the car hadn't been fixed. He said he would get his accountant to EFT the refund on the 11th January in the morning, no payment was made on that day. It is now the 15th and still no refund. He keeps avoiding my calls.