You have several ways to go against the builder when negotiation fails.
You may go to the consumers office (sometimes works sometimes wont)
You may also report the builder to the Autonomous Community. Article 6 of 57/1968 Law was revoked but under the LOE (General Building Act) there are fines up to 25% of the total amount not guarantied by a BG or insurance.
2.- Civil Courts:
If you have a BG or insurance and the deadline for the works to be finished has arrived, the house isn’t finished or they simply fail to provide the LFO (this Law specifically considers LFO a requirement to consider a dwelling finished) and they don’t give your money back plus interests although asked on time (be aware that most BG/insurances will include a deadline to be enforceable) you have a special executive process to ‘execute’ the guaranties. Quite fast process that automatically imposes the court expenses to the debtor. If the completion day hasn’t arrived you have to go to the general process to ask for a refund (cases when completion day hasn’t arrived yet but you may prove is impossible to finish the building) as BG and insurances only become automatically ‘executable’ when the agreed date arrives.
General Civil action, Yes sometimes it goes slow, it depends on the area you are suing. You may ask for refunds, interests, compensations, damages (including moral damages) or building snags/defects. It’s important to tell your lawyer not to be too ‘greedy’ when valuating the economic importance of what is being asked for and to support your claim with solid economic & technical reports as only if you get all or most you are asking for the builder will be ordered to pay your court expenses. The Law (Civil Code, LOE and Consumer-protection Law) is in your side here and, as we say in Spanish, judges don’t tend to see builders/promoters with ‘good eyes’ (belive me, I know what I’m talking of, this is my area)
3.- Penal Courts:
After the article 6 of 57/1968 was revoked in 1995 you may only use this way if there is no BG or insurance, there is no house, and you wont get your money back. Also if you can proof the money you have deposited was not used in the contracted promotion. Criminal Code statues sentences from 1 to 6 prison years.
You may put a denuncia at Police Station or even at the watch court, but if a serious action is to be taken you should start by a ‘Querella Criminal’ (criminal lawsuit) written and signed by a lawyer.
Wouldn’t recommend this way unless strong evidence of criminal offense can be taken to court.
By the way, a 20 year delay in Penal Courts is NOT real
NO Civil/Administrative action by the same issue can be taken if a criminal procedure is being followed by the same things. In the other hand Administrative & Civil actions are compatible.
This is only a very simple overall description of what could be done. You will always first have to talk with your lawyer as he wold have all the details needed and would be the one to advice you the best way