Professional ghostwriter here with 15 years in the industry. I have been on the other side of this exact dispute and can offer perspective from both angles since I now also hire ghostwriters for my own projects.
The entire ghostwriting arrangement hinges on the contract. A properly drafted ghostwriting agreement should explicitly address: ownership and assignment of all rights (copyright transfers to the client), whether the ghostwriter receives any credit or attribution, confidentiality obligations, and what happens if the relationship breaks down mid-project. If your contract clearly states that it is a work-for-hire arrangement and that the ghostwriter waives any right to credit, you have a very strong legal position sadly.
However, if the contract is vague about credit or if there was no written contract at all, things get complicated. Under copyright law, the default is that the author (the person who actually wrote the words) owns the copyright. The ghostwriter would need to have explicitly assigned those rights to you. Without a clear assignment, the ghostwriter might actually have a legal claim not just to credit but to co-ownership of the work.
If you do not have the original signed copy, check your email for any discussions about the arrangement. Courts have found binding agreements in email exchanges, text messages, and even verbal conversations (though verbal agreements are harder to prove). Any communication where the ghostwriter acknowledged that they would not receive credit or that you would own the final work is helpful.
At 73K in dispute, this likely involves a book with significant commercial value. Get a publishing or entertainment attorney involved. Many of them handle these disputes regularly and can often resolve them through negotiation without going to court.