Talk to a lawyer (ask if they'll take a first visit without a fee) and see if you have a case.
When I was waiting for an insurance settlement after an accident, a sister pretty much supported me for over a year covering an apartment and grocery money. We had no written document. When I finally got the settlement money, I asked her to give me a dollar amount to settle things. I thought her number was too low ($6000) so I repaid her based on my calculations ($8000). I gave another relative $2000, unasked, to repay for assistance in the same period.