Could you provide the url to your site? At first impression it sounds like you have some malware on your site. If this is the case, you'll need to take some steps to remove it. The procedure will depend on what plan you are on. Malware is not the only reason this could be happening, e.g., someone actually "forwarded" the domain to that site is a possibility.
I'll keep an eye out for an update.
Hope this helps,
I don't think there is any doubt you've been hacked. I took a look at the source code and the very beginning code is a full redirect. If you are not running a WordPress site, the first place to look is your FTP security. You might want to try to run SiteLock on the site.
I have a feeling that you'll need a clean backup to restore the site to a working state. If you do have a WP site, its time for WordFence.
Wish I had better news!