Garbage drama (literally)

So my neighbor two doors down has been “secretly” adding 2 to 3 bags of their garbage onto our garbage at night on the curb for garbage pick up the next morning. We have several security footages of it cuz it’s been happening for months. Funny thing is they send their kid to do it. We’ve been bringing the garbage back onto their curb which is usually full of garbage so I’m guessing it’s cuz they’ve reached the max number of bags. It’s annoying nonetheless cuz I don’t know what’s in their garbage and it’s not my problem they generate so much of it. We haven’t confronted them so far. Any suggestions on how to go about this?