Apartment Management Came Into My Mother's Place Unannounced To Knock On Her Bedroom Door

Location: Mississippi

Sorry if this is all over the place. My mother has lived alone in her current apartment just over 2 years. She's disabled and on fixed income so her options are limited, and this place was one of the few that worked for her needs. The complex is large, mostly college kids, kinda low-income. Management has quick turnover and from my mothers words, employees are a mixed bag. They're either entirely checked out and rarely show their faces or are too involved. On multiple occasions, two or more members of management have entered my mother's apartment without prior notice, not even a knock on the door. They only entered her apartment to hand her a pamphlet or to tell her about some upcoming event/party that management were hosting. A few of these instances they said they "knocked" but my mother either was asleep, in the shower, or just didn't hear it. From her recount, she'd hear voices or footsteps and fear that someone had broken in (the area she's in is high crime). My mom doesn't own any firearms or a guard dog and can't afford a security system. She'd open her door to find strangers in her living room (again, there's new people working there constantly) sometimes even about to knock on her bedroom door. I know this can't possibly be legal, but even when my mother has filed complaints nothings been done. This keeps happening. Who do we talk to/what can we do to stop this? She can't afford to move at the moment and I can't physically be down there to help her do so, for the moment that isn't an option. Any advice welcome ????????​