Volkswagen weak warranty policy

They fixed my vehicle and I collected it 2days before the factory warranty elapsed, the service provider who handed over the car to me told me that there is a 12 months guarantee period on all parts that they've fixed/replaced. A month later my car had the same problem, when I give them a call to book it in they tell me that I will be liable of the costs, when I tell them about the part being replaced and has a 12 month guarantee on it, they still refer me to being liable of all the costs of I bring it in.