U2715H Horizontal white lines with certain contrasting colours

I'm a UK customer. Ever since I took the screen out the box there have been a couple of issues which have remained to this day (about 18 months later). I cannot find any way to start an RMA on the Dell website. The issues that I have had with the monitor:

1) Interference patterns. This occurs despite testing with two different computers, using two different HDMI cables. The monitor displays strange interference patterns depending on what is on-screen. I've attached a photograph of the effect. You will notice horizontal banded lines, which move around as the windows are moved around, and it's particularly noticeable against solid colours.

2) Occasional and brief flickering of horizontal bands. This occurs despite testing with two different computers, using two different HDMI cables, which leads me to believe the fault lies with the monitor. It occurs infrequently and briefly and it's not something that can be easily recorded with a camera. If I was to describe the issue, I would say that essentially a thin horizontal band of the display flickers and garbles for an instant.

You can see an example of issue 1 below:

In the photograph, the white horizontal lines across the high contrast areas vertically move around as the adjacent windows are moved around vertically.