Nissan NP200 mulfunctioning

I bought a Nissan NP200 in July at Nissan Randburg before the end of July i took the car to them for repairs, again in September the problem was still there i took it back to them it came back in October and with the same problem, again in November i took it to them. but still no joy. in total i had taken it to them 6 times. now they are telling me that they wont take it back for repairs. i want my money back or them to give me another car they are refusing, they are saying this is according to Nissan specification. if i wanted to buy a s**** car i would have gone to s**** yard i came to Nisan with the hope that they are credible but they sold me a car that is a s**** now they don't want to take their car back.