Refund Refusal: Need US Representation

 Legal Issue:

I live in France and in January 09, I made a deposit to attend a self-improvement program hosted by a New-York City based company. At the time I made the deposit, the refund policy (displayed on their website) was that they could hold up to $500 of the money already received. Things came up and I'm now unable to make it to NYC and thus attend the program, but when I ask for a refund they refuse to reimburse me, by giving me false arguments. Moreover, since January, they changed their Terms of Service without informing me beforehand, and now I have no written evidence of what the ToS were when I signed up and they try to use that fact against me. What can I do? I know I'm in my right to get my money(~$2800).
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FIrst Name:Joel
Last Name: Marchand
Phone:
Email: anatolhenri@hotmail.fr
Phone: 0033646496551
Address: 32 gradne
City: Garches
Country: France