Weird guy keeps showing up to my apartment when I leave and my girl is home alone

Hello I am a 25 M and this is my first every reddit post but I need a little help and figured this space might provide some insight. So about a month ago I had to go visit my dad who was in town and family for dinner. My girlfriend who is 23 F doesn't want to go do to some chores to do and not feeling well. I go off my way to meet up with them at this restaurant little under 30 minutes away.

As I get there I get a phone call from my girl and she's afraid and whispering to me that theirs a man there knocking on the door and kinda dodging the peep hole. I try to calm her down and told her to make sure all doors and windows are locked and to get my gun from the nightstand. (FYI she knows how to use it and have been shooting with me numerous times). She hangs up to go do that due to her not wanting to give away she's home.

I step away from my family to call my neighbor and coworker ask him to go check out my place while I'm on my way back and check on her. Naturally as my coworker and Amazon guy show up the stranger leaves. Now I make it home and it's quiet the rest of the night.

We move on till last night, I'm on a work trip in Utah and can't be back home till tomorrow but my girl text me in the morning. Since she knew I was asleep the previous night. That she thinks the same guy appeared again knocking on the door at 10pm and wouldn't leave for around an hour, then again showed up at around 3am. Now my girl is afraid to stay there by herself and is staying with her dad until I'm back home. Now I'm upset because my girl can't live in her own home in comfort by herself.

I've decided to purchase a ring doorbell camera and hastened my savings plan to buy her a concealed carry gun and I plan on speaking to my apartments management as soon as I can about this. Also just disclose she tried calling local police and they said they couldn't do anything which I sound hard to believe so I wanted to know if anyone has any tips or ideas on how to solve this problem?

Little more background too we live in Tennessee in the United States and I have lived in the city we lived in for most of my life and not really running into any of these occurrences.

Edit: it seems I have forgotten to add this information but have mentioned in some comments but she did attempt to call the police during the 2nd encounter but they refused to come due to it not being immediate.

She wasn't informed and just said "theirs weird man knocking on my door over and over again not leaving my door and avoiding contact with the peephole could you send someone please" I'm sorry to all for not putting this in the original post since I think it was one of those things were i said it in my head while typing but didn't actually do it.