Technically if you gave them USD$100,000 and they gave you back USD$100,000 then they have refunded the deposit. They could argue that as part of your foreign investment you took on the currency risk. You could possibly have arranged the USD$ to be lodged in a dollar account here or reinvested elsewhere in the US.
But if you handed over Euros to transact and the firm doesn't hand you back the same Euro amount then you are in a better position to seek the difference, although surely if this was an investment( ..... one of the 81 investors ) then surely you would have sought some independant legal and financial advice, otherwise its pure speculation. and those 81 Investors become 81 Speculators.
Look on the bright side at least you are getting most of your deposit back. You could have blown it instead on the stock market in the same period and be down to pennies.
But talk to Joe on 1850715815, apparently he can do anything, starting runs on banks, building hospitals wards out of prefabs, he may even get you your money back.