Pls help!!!!!

I have recently bought my Audi Q7 from USA and i am on the other side of the world where has no Audi dealers in my area but only Volkswagen dealer. I am facing a problem with my tailgate where it doesn't open all the way up but only till not even half way, so i have brought my car to the volkswagen dealer to get it diagnosed with their computer system and they said there is nothing faulty about the motor that lift it and they did reset the opening position to open all the way up and right after its set the tailgate works just fine but about after 20min or so it goes back to normal and wont open again. I have tried to reset the door manually as they suggest to do so by lifting the door to my desired height and press the closing button for 4sec whatever, but it doesn't do anything. Now i have no idea what to do please please help,