Yes, you have a case for the $3750 purchase price and your 25% of net profits. How long you get this net profit share, whether you're also entitled to an accounting of the net profits, whether your contract entitles you to attorney's fees to the prevailing party, and any other remedies, etc., depends on what exact language is in the contract you signed. That document should also contain a forum selection clause that specifies which state's law governs and in which court you have to sue.
If you haven't sued anyone before, see a business litigator for help.
PLEASE READ THIS BEFORE YOU COMMENT, EMAIL ME OR PHONE ME. I'm only licensed in CA. This answer doesn't make me your lawyer, and neither do follow-up comments and/or emails and/or phone calls --- we need an actual agreement confirmed in writing before any attorney-client relationship is formed. Please don't expect me to respond to your follow-up queries. This answer doesn't constitute legal advice, and shouldn't be relied on, since each state has different laws, each situation is fact specific, and it is impossible to evaluate a legal problem without a comprehensive consultation and review of all the facts and documents at issue.