Literring garbage in a private property for several years

My next household has three floors occupied by same family , their kids litter my property on daily basis . This is ongoing for several years now .When asked not to litter garbage they refuse to own up that it was done by their kids instead use fowl and abusive language . No body in my family wants to take any action as they don't want to get abused ,they prefer to get it cleaned up and want me to ignore and keep quite . I want to take strict action against people who disrespect my right as a ow