We ‘accidentally’ tried the criminal route.
The lawyers we appointed to take our case to the Civil Court took it via the Penal Court against our wishes. It was kicked around the court system for a while, rejected on technicalities a few times although no-one bothered to tell us about this. We were warned it could take 20 years and that may be true.
We were advised (wrongly as it turned out) to make a denuncia to the police in addition to the proposed Civil action. The lawyer wrote this and we took it to the local Guardia Civil. One officer looked at the details which included the name of the representative of the developer and said (approximately) ‘Oh I know him. He’s a very nice man, I don’t think he’d do this.’ What hope do we have?
I believe that the best route is probably via Consumer Law in the Civil Court.