This requires a complex answer so I will cover the basics here. Immediately I see a potential statue of limitations problem. Most states have a 5 or 6 year statute of limitations for contract matters. This means that if more than the allowed time has past, and you have not filed any legal action, you would then be prohibited from doing so. When the contract was formed and when the breach occurred are two important issues in SOL matters.
If you could still file a lawsuit then you would have to first look at any written contract you had with the Vendor, which is likely found in their terms of service or other disclosure by them that you agreed to. The matter may be required to go to Arbitration or there could be a clause that states where any arbitration or court action must take place.
If this is a legitimate investment firm then you also might be required to go through mandatory arbitration.
Next you must study the contract and see which sections were breached and then gather proof of your case. The amount of damages is important as it will determine which level of court this would be filed in.
If you have worked through all of these issues and you can file a suite, you have to know where and who to serve with the summons and complaint.
If they are claiming to be an investment firm and they are not registered with the SEC, you could also seek the help of the SEC. You could file a complaint with the SEC even if they
are a registered investment firm.
I hope this gives you a start and that I have answered at least some of your questions.
Best:
George D. Greenberg, Esq.
www.attorneybitcoin.com 
