Your result
Spain — Diaspora & Religious Return
Possible
A refusal under that law is worth looking at again, because a good many turned on the evidence rather than on whether the applicant was in fact Sephardic.
The law asked for two separate things: proof of Sephardic origin, and proof of a special connection with Spain. Both were assessed on the documents as a whole rather than against a checklist, which meant the outcome often depended on how a file was assembled. Refusals also arose from the twelve-month decision deadline passing without an answer, which counted as a refusal by operation of law rather than as a judgment about the person.
Which of those happened to you matters, and the refusal document says. If the file lapsed on time rather than on merits, that is a very different position from a reasoned rejection. Either way, whether there is anything left to do depends on the dates and on what was decided, so this is a question to put to someone who can read the decision itself rather than one a page can answer.
What is definitely still open, and is unaffected by anything that happened to that file, is the route in the Civil Code: someone of Sephardic origin can naturalise after two years of legal residence in Spain, against ten for most applicants, and is expressly exempt from renouncing their existing nationality. It requires living in Spain, which the 2015 route did not — but it is permanent, and nobody can close it on you.