If you have properly performed your work and your client has accepted it without suffering damages, you are entitled to payment. It is best not to disclose identities of offending parties in a public forum, but rather to deal with it through the legal process created for resolving disputes.

You have indicated that both you and your client are located in Maryland. Consequently your courts probably have jurisdiction over the person of the defendant. The dollar amount of the dispute seems most likely a small claims matter which can be tried by the court within just a few months for the minimal cost of the court's filing fee. Depending on Maryland's rule of civil procedure, the court will probably award you the filing fee as part of your judgment if you win. The actual trial will only take a few hours...most of which will be spent waiting to have your case called rather than in the actual trial. The trial itself would probably take no more than a half an hour.

You have strong claims for contract breach and unjust enrichment. Your client has also accepted the benefits of your work, and is now estopped from repudiating the validity of your contracts.