I do not practice in MO so cannot advise you specifically as to how this debt may or may not be pursued but here are a few things for you to consider. You do not come to the table with clean hands since you were aware that this was not a licensed lender and yet you availed yourself of their services when as you described you were in a "desperate situation". Lenders are never in the business of loaning money out of the goodness of their hearts- it is always a business deal designed to make them money, whether its a bank or otherwise. That is where interest comes in. Perhaps family will lend money to you interest free but in this case clearly you were not able to go that route. They provided a service to you when you were "desperate" they should be paid what they and you bargained for.
Disclaimer: The foregoing answer does not create an attorney-client relationship with Attorney Cannella or her firm. This answer does not constitute legal advice, is provided for informational and educational purposes only for persons interested in the subject matter, is not legal opinion, nor confidential in nature. Each situation is fact specific and may be subject to state specific laws. Without a comprehensive consultation and review of all the facts and documents at issue it is impossible to evaluate a legal problem fully.