I contacted the guy - he did not respond yet. But as a reaction(?) to my first e-mail where I told him, that his app is a GPL violation he first added the whole original description from my app including the links to my website etc..
Now I also wrote Google about this case and I wrote him again that his change makes the situation even worse as I was now in the situation that there is Google Play entry telling that this specific app "PERIOD TRACKER" published by me - which is wrong. And again no sources of course. I told him, that I contacted Google and also my laywer - just in case, it is needed.
Then I also found out, that the app logo was obiously copied from the website of Boots UK and the Google Play entry indicates that the app uses Ads - which is a violation of the legal terms of Boots - they do not allow to use their content for commercial purposes. So I also contacted Boots and made clear that I am not responsible for this illegal copy. That's the reason, why I am now also in contact with my laywer to avoid any legal problems.