I can't imagine how I can influence its DNS or redirection?
You won't be able to stop the requests coming to your server but you can control how your server responds. That's all you need to achieve both options I've already suggested.
1. Is the server running Windows or Linux?
2. You have full control over the server? Root access?
3. Which HTTP software do you use? Apache/nGinx/lighttpd/etc.
There are people here on the forum (myself included) who you can pay to do it for you if you want. It's not something too technical though so you should be able to figure it out with a bit of reading. You could search for "redirect domain to another" along with the name of the HTTP software you use. That should give you a few guides.
Edit: The HTTP headers from your site indicate you are using nginx. Assuming that's correct then
this guide should help.