Complain / unhappy customer

Bought a car at avura motors rustenburg waterfall mall the car started making noise found that the rear bumper is loose it has been reworked but i was not informed of the work done and it has a Dekra sticker how is that possible it could have been picked up during testing. The manager is not helping at all they want to fix a problem that can not be fixed it has to replace. On the sales documents there is no where that the dealer is stating that the car was in an accident or not but according to inspection done at Audi rustenburg and roodepoort 2 technicians and a panelbeater confirmed the car has been in an accident whether it was a small or big accident but as a customer they should have disclosed that.