Hyundai refusal to correct their mistake

More than a year ago I took my car for a service and paid for a windscreen wiper to be changed. They put this in incorrectly which scratched my windscreen. I asked for both wiper and windscreen to be replaced and they have only replaced the wiper. They have refused to replace the windscreen even though their bad part and workmanship has caused the problem. Each department sends me to anther department. This was not the only problem with the car which is fairly new: paint peeled off the boot and rubber at back door came off. Both these were redone but I didn't have a car for more than a week due to their poor workmanship.