Neighbor opened my mail

I'm not sure how to react to this situation. A client sent me a holiday thank you gift, but unfortunately, I moved to a different unit in the same building this year, and he didn't have my updated apartment number. The package room attendant mentioned that the resident in my old apartment and I share the same first name, so he wasn't sure who it belonged to (no blame on him). One of the residents accepted the package, claiming it might be their partner's because of the shared first name. My last name was on the package, but that didn't seem to matter.

After discovering that my client sent the gift to my old address, I managed to have the mail room attendant track down the box and retrieve it, but it had been opened. Since it contained sweet treats, I'm not sure if anything is missing because everything inside is individually wrapped. I'm frustrated because it seems clear they had no intention of returning it. They accepted the package last Tuesday, and I'm writing this on the following Monday. I feel like I need to just accept it for what it is, but people can be really strange. I can't imagine taking something that I know doesn't belong to me. Even if I were unsure, I wouldn't do it. Maybe that's just me. Do you have any advice on how to deal with these neighbors?