Any UK government website ends in .gov.uk
Similarly, any US government website ends in .gov
Your link doesn't, so I'd be worried!
http://www.usembassy.org.uk/americanservices/?p=519
This is where you should have been:
https://esta.cbp.dhs.gov/esta/
The domain name you've provided has only existed since Thursday! It was created via GoDaddy (which is an excellent service for people setting up personal websites but hardly ever used by reputable firms, since they employ proper web designers) and is a 'private registration', which hides the identity of whoever registered it.
I'd guess that you've lost your money and, more worryingly, given your debit/credit card details to someone whom you'd rather not let have access to them.
Notify:
1. Your card issuer ;
2. The official UK police anti-fraud website:
http://www.actionfraud.police.uk/
3. GoDaddy (who, as well as providing the domain name, are hosting that website on their servers):
[email protected]