Unfortunately, there are situations that we don’t see and then it becomes difficult to find someone to blame. How many of us haven’t “reached the foot of the car” and noticed it was scratched or damaged? know what to do…

Car scratches and you don't know who did it?  know what to do...
Did you leave your car parked in a parking lot and when you arrived it was damaged?  Faced with such a scenario, the most natural thing would be to get very upset, and perhaps even call the police authorities to the scene.
And this is what you really should do. First, leave the car alone and take a few pictures showing evidence of the damaged areas..  immediately Contact the police authorities to do Report the claim and later use that record to hand it over to the insurance company.
Until the arrival of the police authorities, Find some witnesses.  Record, if possible, the name, citizen ID and mobile phone number and try to understand if the witness saw anything unusual.

If the car is parked in a public park and there Surveillance Cameras Authorities can use these contents.  On the other hand, if it is in a private garden, according to Article 167 of the Code of Criminal Procedure...

Photographic, cinematographic, phonographic or electronic copies and, in general, any mechanical copies are valid only as evidence of facts or objects reproduced if they are not illegal, under the provisions of the Criminal Code.

These records can be requested through the judicial process.  After the previous steps, if it makes sense, contact your insurance to see if they cover the damage.  If you do not agree with the insurance decision, you can always appeal to the insurance company Arbitration Information Center in National Consumer Disputes.