Problem with Nissan Qashqai

I bought a Qashqai from Mccarthy Nissan Randburg. It is a 2l with CVT gearbox. When I drive the vehicle and want to accelerate, the vehicle loses power, drops about 1000 rpm's and then starts to pick up refs again. When I want to accelerate on an uphill or on the highway, the vehicle refs up to around 6000 rpm and stays there until I take my foot off the accelerator. This does not seem normal and the vehicle is very heavy on petrol.The workshop manager told me that is seems that the gearbox is faulty after he took the vehicle for a drive. Mccarthy Nissan said that they took the vehicle to Mayfair Gearbox but was told that it is not the gearbox that was faulty but the ECN. I was told that they re-programmed the ECN and the problem has been sorted out, but I still have the same problem. Can Nissan South Africa please assist with this? They also replaced my rain censor with a new one, but it also still does not work. Maybe they just need assistance from somebody that knows the vehicles.