You might try making a Denuncia (crime report) alleging fraud.
You can make the report on 902 102 112 ask for English when you get through (its a 24/7 service).
They will probably tell you if it is a crime or a civil debt.
If they take the details, you will need to tell them which National Police Station you wish to sign it at, then do so within 48.
Don't forget to take your Original Residencia, if it is still valid, if not then you Original passport.