So many A4's with the 2.0T petrol engine seem to have either a moderate or major thirst for oil. Mine uses around 3L every 15 000km. Some cars use up to 1L per 1000km. This is stated in the owner's manual as "acceptable" oil usage. But it is not. Request from the dealership to perform an oil consumption test. They fill the oil and then you return in 1000km and they measure the consumption. If it is way to much, they may take action and replace the piston/rings etc.
I also find it unacceptable that a modern engine can use so much oil. This means on a trip from JHB to CT, you would run out of oil just past half way - ridiculous!
If you just purchased the car, I would fight harder with them as it is clearly not you that caused the problem and they need to address it as a defect within 6 months of purchase.