Refund or New engine.
Not sure if oil additives 'add' any value over a good quality oil.
Also this has now altered the test results, you need to watch the oil consumption with what the Manufacturer specifies the vehicle needs.
I haven't seen VW promoting oil additives either. This adds additional costs onto your servicing as well, it isn't your fault the car is consuming oil so should you really be responsible for these additional costs? I know the cost of Oil additive probably isn't much but it's more the principle in finding a proper solution.