Volkswagen
VW can't fix their own product

Good day,
i bought a brand new polo vivo GT on the 05/04/2012, at the mileage of 4000 km it stated making a knock noise on the front right Tyre. i then booked it for check up (The Glen) a technician drove with me and said it is normal.
when i took it for 15000km service (Booysens) i reported it again a technician said there is nothing wrong about it however when you drive it you still here the irritating noise, i booked it again for 30000km service at (The Glen)
they admitted that my car does have a problem that i've been complaining with. at first they said that the engine mountains and Gearbox mountains were faulty and replaced (18/06/2013) problem not resolved, two weeks after i took it back again they said the problem is shock ab-sober (16/072013) and it was replaced the problem still not fixed.can't believe VW are failing to fix their own product. can i return back this car and get another one or cash back?
which VW branch is the most recomended?
please advice