How would you react to this?

So my boyfriend and I lived in this apartment that was above 2 girls who were constantly getting into our business. They all used to be friends, and when I started dating him, they completely stopped hanging out with him, but they'd say hi and completely ignore me. They did inappropriate things like sending text messages that had the word "" in it, and they would text him when they knew it upset me. One day I overheard them talking about how they thought it was funny they could get under my skin, so to get my boyfriends attention they put two lawn chairs right in our driveway and laid out in bathing suits and waved at him and stuff. Then they got a baby kiddie pool and put it right by our steps at the bottom or our door and sat in it, and talking to him. Now we moved. We completely switched apartments. But now, she's bringing over my mail to him and talking to him still. My mail would have been in the new people's mailbox, not theirs, and they completely just did it on purpose to get to me.. What would you think and do about it?