Hello, We understand how upsetting screen issues are. For issues with grainy lines or dead pixels, you can find some steps here that may help. First is to see if third-party apps are causing this behavior, using Safe Mode. If the display is better in Safe Mode, then uninstall apps until the display is not grainy: https://www.samsung.com/us/support/answer/ANS00062983/
When troubleshooting is not helpful, it is recommended to have the phone evaluated by an authorized service center. You can use the following link to find a list of service centers in the U.S.: http://www.samsung.com/us/support/service/location or by calling customer support at 1-800-726-7864. There are also the following options: 1. Facebook Messenger: http://m.me/samsungsupport
And you haven't had another problem with touch about how sometimes it doesn't respond to the touch to the first action if not until the second attempt? when you change the window and swipe right, when you open the app menu or when you press the send or open button?
