Sold a dud car from a an Audi certified pre-owned dealership

I bought my 2011 Audi A4 (second hand for +-R160,000) from the Audi Northcliff Certified Pre-Owned dealership less than just two years ago. I took my Audi in for its 100,000 KM service and was told that the car needed a new timing belt, which I had no choice but to replace (and amounted to R25,000 after a kind discount). I then took it in again just one month later because it was having oil issues. I was shocked (but not shocked at all) to find out that I would now need to replace my pistons for a grand total of R75,000. I bought the car thinking I was buying a "quality vehicle" from a "quality brand"; instead I am now in the position whereby I have to spend a total of R100,000 give or take, on a car that I bought two years ago, which has a resale value of R90,000.