Poor response from VW South Africa

I bought a VW Touareg 2011 V6 TDI last Year in June, within 2 month the Booth Lock broke (a small nylon plastic part). When i inquired if a lock is available the VW dealer informed me that there is no stock in the country. I sourced a new one by searching in the Pretoria and JHB area. It was installed by my qualified Mercedes Diesel mechanic, which was 30 Years ago the apprentice of the Year. 10 month later the exact same part broke again, which to my knowledge verifies a product failure. Since this is not acceptable to me i contacted VW SA Headoffice, after a view e-mail back and forth, they declined any responsibility due to that the part has not been installed by a VW dealer, which is a lame excuse. To install a booth lock, you don't need to be a brain surgeon, i could have done it myself. I got a quotation from a VW dealer, the cost of the lock is R 5'000 plus R 1'000 labor, which is not acceptable to me, considering that the plastic part cost maximum R 10. The 2011 Model was the first one installed with this type of lock, i still have to find out if any later models have been fitted with this type of lock or if it has changed, which i will follow up. I am also investigating how many owners had the same problem. It is curios that there was no stock a Year ago and i am wondering if there is any stock at the moment. It is a great car, but in this price range i do not expect a cheap plastic part in the booth lock. I am disappointed, but will follow up with VW Germany to see if they make the same lame excuse, which i am very doubtful.