This feature is available with some paid plans
To find out who your domain provider is, use a website like DomainTools or the WHOIS Lookup provided by ICANN. Information like the Registrar or Name Server can be indicators of your domain's provider.
Another, more technical option is to use your computer's Terminal program to look up the domain's name server. To do so, type in dig -t NS [your domain]. For example: dig -t NS bitly.is. A domain's name server can be a good indicator of the domain provider, but it depends on the provider's naming methods.