Tenants spitting and throwing dirt in my private garden

My family owns and resides in a ground floor flat with our own private garden. There are tenants on the First and second floors of my building (The respective flat owners have rented their flats to these tenants). Now these tenants spit and throw garbage in my private garden boldly. Almost daily I’ve seen them spitting and throwing garbage like cigarette pieces, hair, wrappers, condoms. Spitting is supposed to be a criminal offence but they boldly spit in my garden. When I confronted them they boldly tell me “Go do whatever you want”. When I complain to the society they either do not respond or refuse to take any action. Neither does the respective flat owners that rented to the tenants bother to do anything when I complained to them. We are fed up of this harassment and are like prisoners in our own house and garden. I need to know which authorities I can escalate this issue to and also is there any online media channel where I can highlight my grievance.