Name server changed without my Consent- help me

Someday ago I got one mail from Hosting Service provide stating that
"We have received a request that the name servers be changed for the following domain name(s):www.mydomain.com (original domain name changed)”
I did not request anything from them; I can open my hosting account and can make necessary changes. my domain is 3 months old.
Is someone trying to still my domain or anything else? What should I do? Can anyone explain me what is going on?

Login to your DNS registrar (DO NOT use the link from that suspicious mail) and check DNS server configuration. If it is not what its supposed to be - change your password ASAP and report this.

P.S. DNS update propagation takes time, so the fact that your site is still there does not mean anything.

Yes, you should check your DNS settings within your DNS registrar control panel. If you suspect any theft attempt, then report it directly to your domain registrar.