My phone was stolen in Athens Greece, how can I know the IMEI of my device without packaging box？My device is already offline

My phone was stolen in Athens Greece, how can I know the IMEI of my device without packaging box？The day before yesterday, iCloud locked the location of my stolen phone. I also asked the police for help, but I didn’t know the IMEI and couldn’t obtain evidence, so the police couldn’t help me.My device is already offline today.How can I continue to trace the whereabouts of my cell phone?