How do I unlock the sim card on my old Android phone?

[AC Question]

I thought I had lost my phone and that it was then stolen. I reported the phone as "lost or stolen" on my carrier account and even reported it to the local police as stolen. Needless to say, I found my phone. It was not stolen. When I go to my carrier account to try to swap to that phone, it says the SIM card is already in use. !? I don't know what to do now. Can somebody help me?

 

[the tall guy]

Speak to the carrier, they are the ones that block the sim. Also probably best to let the police know so they don't waste anymore time on this case.