Someone is stealing my site

It has come to my attention that GreenCarReports.net (https://whois.net/whois/greencarreports.net) (https://www.whoishostingthis.com/greencarreports.net) have made an unauthorized use of my website ElectricCarsReport.com.

Actually, he has stolen all of my 3.5 years old site. I’ve contacted the site owner and his hosting company but there isn’t any response. How can I stop this? What am I suppose to do?

I’m changing my FTP password 1-2 times per week.