Screen is grey with many little dots

I have a Fairphone2.
Very irregularly, but also quite often, when I want to use it, the screen is grey with millions of dots.
To gave evidence, I made some picture but this list does not allow attachment.

The phone is NOT usable then. This is extremly disappointing for me, because i thought I get a reliable phone when investing 500+Euros!

Also, I do not find any address to send it back for repair
I am still within a warranty period, and if this problem does not get fixed I want my money back.
Where can I turn to??

A post was merged into an existing topic: Noisy coloured pixels on my Fairphone 2