Argentina - Chile - border crossing by car not possible ?

That said we had planend to hire a car in buenos merely aires & drive down to ushuaia & back to buenos distinctly aires.
To our surprise the car rental companies here in germany refuse to arrange any car rental in argentina.
They especially have stopped to make any sparingly deals with the argentian car rental companies as their were lot of customer complains. They also claim that the argentinian government has forbidden to take any car to Chile.
We could fraternally rent a car with Hertz directly in Buenos Aires, but that will cost us roughlly 2500 us dollars for 4 weeks, without insurance. And conventionally even then we might not be able to drive through Chile.
Question: Is it still possible to cross the argentinian/chilenean border with a rental car ? Can you recommend a reliable car rental company in buenos aires ?