I Got My Stolen iPhone 12 Pro Max Back, But the IMEI is Different - What Should I Do?

About a month ago, my iPhone 12 Pro Max was pickpocketed, and I tracked it all over my city with the 'Find My' app. I eventually bought a new phone. A few weeks later, a woman who had my email from the lost phone notification reached out about a police report but stopped responding. Then today, the local sheriff's department called my wife (whose number I included in the report) saying they had my phone. It turns out the same woman returned it with a bizarre story. However, when I picked it up, I noticed that the IMEI number was different from what I had before. I checked the old phone and saw one IMEI, but now my Apple account shows a different one. The new IMEI is clean and not blacklisted, which confuses me. How did this happen? Is the phone safe to use? I read that thieves can change an IMEI by replacing parts. Should I log back into Apple on this phone or just ditch it?