Audible Promotion Disappeared and Original $0 Trial Offer Is Unavailable

I am writing because I am very frustrated with my recent attempt to start an Audible membership through Amazon. A few minutes ago, I saw an Audible promotion that clearly showed the first book for $0 and then, as I understood it, either $0 or $0.99 for the next few months before the normal, higher price would begin. While trying to sign up, the offer disappeared, the price changed, and I could not complete the sign‑up under the terms that were originally shown. Now the book I tried to get for $0 appears in my Prime/Audible library, but I am not sure how it was added and I am concerned that I may be charged in a way I did not intend. I am not looking for a long explanation; I simply want help to get back to that same promotional offer and to receive the book on the terms that were advertised (first book $0 and the discounted trial period). I kindly request that you correct my account if needed and enable me to start the Audible membership again with the original promotion so I can purchase and use the book as initially offered.