Hello Iswood, so sorry to hear about your situation, and I must say that for them to screw you over like this is ridiculous. Slap them with a lawsuit, and good luck with it. I can't give any useful advice here but explore all of the options, which might be:
1) Speak to the American Embassy to see if they have any advice
2) Try consulting with other attorneys, such as the American attorneys listed on the Embassy website.
3) Use the media as a leverage, tell the company that you'll begin contacting American and UK media, to me this seems a story that they might want to avoid.
Shocking treatment, they should be hung out to dry. Please let us know how you get on? If the situation came up with someone else, any information would be extrememly useful.
<a href="
http://www.usembassy.org.uk/">US Embassy London</a>
Another site might yield some information to you, the forum at
<a href="
http://www.americanexpats.co.uk/">American Expats UK</a>
Best wishes, thoughts, and prayers.
Leah