Ugh. What a hassle. Hate to hear that.
When I graduated college, my dad's graduation present was signing over to me a small rental house he'd had forever. He'd rented it to a couple for several years and then finally sold it to them owner-financed, with the stipulation that I was now the owner and would collect payments. I was moving to Austin, so I set up a collection account with the local bank for them, so they didn't have to mess with mailing anything (this was before PayPal and a lot of other methods available today, not that that couple would've probably been capable of handling PayPal) and I didn't have to mess with getting money from them. All the responsibility for upkeep was theirs, and the property reverted to me if they defaulted. It was pretty low-value property, but I sure thought it was a heckuva gift from dad at the time.
They'd rented from him for years and he never had any problems with them. Neither did I, while I was still in town. The man was a veteran with a VA disability check and some measure of retirement, so their income was stable. As soon as I moved to Austin, their payments were hit and miss, they wouldn't answer their phone when I called, and while I was loathe to bring my dad into it, I had to get him to go and collect for me a couple of times, because driving 5 hours to do that was just not an option. One day after having more trouble with them, he went to see what was going on, and called to tell me they had cleared out, stolen the window units, damaged a few other windows, and that I needed to come home to seal the place and do whatever it is I was going to do with it.
Don't even have time here to explain what a hassle that was. Had to spend a week to go home and do some emergency work just to keep the bugs and animals out. But it appeared there was a mold problem at that point too. I didn't want any more of owning a place I didn't live near to keep my thumb on things, and I didn't have the time or will to deal with any mold issues. I put it up for sale and wound up taking a bath on the value (though, again, it wasn't that valuable). It didn't cost me, per se, since I hadn't paid anything for it, but the opportunity cost was high.
I think if I ever do any more rental property, I don't care if it's next door, a management company will handle it. I'm not in the mood to deal with the idiots in the world.
All that to say......how crappy that you did use a management company and still have this headache. Jeez.