Paying for problem serfaced before warrenty expire

Since the day my Nissan Micra was bought I've been struggling with same problem. <br> In 2012 the engine light came on 3 times and Kimberley Nissan told me there is nothing wrong - just some dust. In 2013 the engine light came on 2 times,yet again I was told nothing is wrong. After 30000km service in August 2014 the car started to misfire, by the third time I was stranded they replaced a spark plug and the wiring at petrolpump was fixed. <br> About three weeks after 45000k service in June 2015 the car started misfiring again and they told me one of the spark plugs is faulty. I was told that it may be external factor that could cause the problem, nothing inside the engine. They replaced all three spark plugs (to my discovery later that it was yet again the same one that misfired). I had to pay since my car's warranty expired in May 2015.<br> After three weeks the car misfired again and engin light came on, took it to Menlyn. The computer tested negative for misfiring, now suddenly the injector is the problem. They swapped the injectors now I have to drive with the car to see if the same thing happens. Sitting with unreliable vehicle and problem that sould've been fixed with 1st occance.