Same problem every 2 months and Audi wont repair

I bought a new Audi A4 in November 2013 and in November 2015 my 1st injector failed. It was repaired after a 3 day wait and in January the 2nd injector went. Again after 2 days the problem was fixed. I asked if this problem would occur again and was told that it is mechanical and they can only fix what is broken. Last week, the 3rd injector failed. This time it was fixed in a day. While the servicing branch has each time fixed the problem and I am told that it is a different injector each time, it is extremely inconvenient not having a car every 2 months. When I raised this with Audi SA they told me there is nothing they can do and if the 4th injector fails in another 2 months I can contact them then. This is not fair.