Car Jacking and cuts off

I bought an opel corsa essentia 2011 model at Williams Hunt, According to Williams Hunt bellville, the car had an engine problem that was not disclosed to me when I purchased the car. few days of driving the car,the Revs were going up abnormally as if you are driving with low speed at a higher gear and the car was jerking showing the Engine diagnostic sign.I took the car in for repairs,they said there's nothing wrong, insisted that they test drive the car and they finally agreed with me and they said its an engine problem...they fitted new engine .the car continued with same problem...they said it was supposed to be reprogrammed after fitting new engine.....they reprogrammed...the problem persisted and now they are telling me that its electrical problem......to me it seems as if they do thumb suck come up with any fault they can think off just to make you go out of their site..I am really disappointed with Williams Hunt service. no one wants to take the responsibility,they sending me back n forth