How to find out who is hosting my Wordpress site?

You need to check the DNS the domain name is pointed to. You may check the nameservers (=DNS) in public Whois database: https://www.whois.net/

Also, this resourse should help: http://www.whoishostingthis.com/

I have used quite a few, but depending on the database they work with, some deliver wrong info. The best one currently is Hosting Checker and Who Is Hosting This comes second.