How to disable lost old iPhone??

Quite awhile back I got a new iPhone and my daughter used my old iPhone 7 on wifi only. Then she lost it. Today I receive a text from someone who found it, and apparently he tried to unlock it because I received text messages with messenger verification code. He is texting me from a different phone; not the iPhone. He described the iphone to me with the specific pop socket on the back, and I assume my phone number came up on the phone as the contact number since it was reported lost.

anyway - this guy is weird and seemingly will not take it to a police station for me to pick up, so perhaps he is up to something. I am done communicating with him.

***Is there a way for me to permanently lock or disable the iPhone so he can’t use it? It’s still linked to my appleID, but is not connected to my data plan.