I must pay for FORDS FAULTY PARTS

My wife has a 2014 Ford Fiesta 1.4 Ambiente which has a factory fault on the door locks which nobody communicated to us even when we had the car serviced at a Ford Dealership in December. Friday they broke into her car and stole her handbag and wallet without any trouble as we saw it on CCTV footage. Now I asked them to replace it because it was not my wife being negligent but a fault of the car and they are telling me I have to pay R1800 to replace their FACTORY FAULTED lock. Why should I pay if you put faulty parts in your cars. I will never in my life buy a Ford again absolutely useless.