Neighbor's gutters overflowing directly onto our egress window
We live in a community of townhouses in Chester County Pennsylvania, and we own our unit. The unit next to ours is owned by a landlord who is renting the unit to a nice couple. The issue we have is that the gutters of the neighboring unit overflow anytime there is any rain. I'm talking full-on overflow, as in: none of the water seems to be making it down the gutter spout and is instead ejected out and directly onto our basement egress window, which has already caused issues with water leaking into the basement.
We've tried speaking directly to the landlord when we saw them outside a couple of months ago, but they brushed it off, saying: "We have gutter guards." I told them that the gutter guards must not be working because the gutters overflow even in light to moderate rain.
They did not take action, though, and recently we've been getting a series of more significant rainfall events, where literally dozens of gallons of water are being dumped from their gutters directly onto our egress window outlet in a relatively short period of time. I have several videos of this happening, but due to subreddit rules, I cannot add them to the post.
Normally, if we are home during these significant rainfall events we can help to remediate the issue by setting up a temporary pump in the area where the water lands and pools, but we're unable to do this if we're not home, or if we're sleeping when the rain happens. I tried emailing the landlord explaining the situation and expressing my concern that this has the potential to cause significant / expensive damage to my basement, but they did not respond. I tried calling them, and it went straight to voicemail. I left a message and they did not call me back.
What options do I have? Is there anything I should be doing from a legal perspective?