Your result
Spain — Citizenship by Descent
Possible
A refusal under this law is worth a second look before you accept it, because a good proportion turned on evidence rather than on eligibility.
The route required showing that the ancestor you claimed through had lost or given up Spanish nationality as a consequence of exile, or fell into one of the specific categories the law listed — the children of Spanish women who lost their nationality by marrying a foreigner before 1978, for example. Refusals commonly came down to the exile link not being documented to the registry's satisfaction, rather than to the family history being wrong. If that is what happened to you, the question is whether better evidence exists: consular registrations, records of a refugee or exile organisation, ship manifests, or documentation held in Spanish archives.
Whether anything can be done with better evidence depends on where your file ended and how long ago, so this is a question to put to someone who can look at the actual decision. Bring the refusal itself — the reasoning in it is what determines whether there is anywhere to go.
If the refusal was on the substance rather than the evidence, the residence route remains open and is unaffected by any of this: a grandchild of someone originally Spanish can naturalise after one year of legal residence in Spain, and a twelve-month job-search visa reserved for children and grandchildren of Spaniards by origin exists to get you there.