Please, please, please.....you must report these incidents to the local Police. I know it can be difficult with the language problem and maybe you might feel prone if your property is not classed as 'legal' but if these low life feel that no one is going to bother calling the police and they continue to get away with it then the situation will only get worse.
Plan what you would do in this sort of situation in advance. Get the 'phone numbers to hand and practice what you need to say. Have your finca details ready with the polygon number so they can find you. At the very least report the incident the following day in person at your local police station. You never know, the police may be more helpful than you think!