Should I Get The Police Involved Or Drop It?

Hi! Im coming here for help because i’m truly at a loss right now. Im sorry if this is confusing.
Location: Arkansas
Im adopted, and when I lived with my “parents” I would receive a social security check every month. My adopted dad would cash it, and send me a separate check to the people I was with because I wasn’t living with him. He told me that they ended when I was 18, but I kept getting them past my 19th birthday. Then they stopped randomly and I assumed they were done, me and my adopted dad had never gotten along, and around then we had a falling out. I moved to Arkansas, and he was in Oklahoma. Fast forward to now, Im 21 and he died last month. My adopted sister reached out saying she opened some mail “thinking it was his”, (even though it was addressed to me?) but it was actually mine. She read it and said that it was from social security and I was owed 350$. That is the same amount I used to get monthly. I was obviously confused because I thought that ended?
I asked her to send me the letter so I could read it myself, but she “lost it” apparently.
So I went to a social security office and asked them about it, they confirmed they owe me money, and said I would need to bring the letter so they’d resend it to me. I signed some papers changing my address, and asked if I had been receiving money all this time, and they said yes. I have no disabilities he could claim (not that i’m aware of) and no reason to why I would still be getting these checks.
I was just going to happily accept the money, but my boyfriend and his family say I should do something about this, I argued he’s dead now so theres not much I could do anyway right? They brought up getting my sister into trouble for the mail she knowingly opened, but is that even worth it? These people treated me horribly, and a part of me would love to be petty, but I feel like none of it will even matter to the police. Any and all advice would be appreciated, thanks for taking the time to read this.
Edit- I tried posting this to r/ social security but it was removed so I don’t know where else to ask.