Qashqai still not repaired

I bought a Qashqai from Mccarthy Nissan Randburg in October 2014. My car has been back to their workshop a few times to do repairs. The last time my vehicle was there for a full three weeks and they promised me that all has been repaired, but they still did not fix all the problems on the car. I even raised it with the dealer principle Dean. My car loses refs when I accelerate, The vehicle has a loud humming noise when I go above 60 km/h, the windscreen leaks water when it rains, the rain censor does not work after they said they installed a new one. They have replaced my buckled mag wheels and usb port on the radio and seems to have repaired the sub frame. I again e-mailed the secondhand car manger Henry and dealer principle Dean last week, but got no response from them. I NEED SOMEBODY TO ASSIST ME WITH THIS PLEASE! I paid a lot of money and this is the service I receive from Mccarthy.