tires and brakes wearing out

We are having problems with our tires losing pressure. Although the car is still under the manufacturer's warranty, with only 15,000 miles when we started to have this problem, they will not give us new tires. Service department says there are two punctures in both tires' sidewalls. We have no idea how this would have happened and believe it to be a manufacturer's defect. Our daughter is having a similar problem with one of her tires on her 2015 Optima. We purchased a long term service contract, which we wanted to make sure would cover the car bumper to bumper for ten years. Unfortunately, the tires aren't covered under that either. There is a SPECIAL service contract for just the tires, of which we were never informed. We are just wondering if others are having this problem with their Kia Fortes or other KIa models.