How is my stolen iPhone removed from Lost mode and Find My with all the passwords and security?

so my iphone got stolen and the morning it got stolen i was able to put the phone in lost mode because it was still turned on...but later on the thief turned it off and it was showing its last location for a while but after 24hrs it just showed "offline" and "no location found" on find my...im so frustrated,my genuine question is this...with all the security measures apple offers and all the two factor authentication plus lost mode that i put the device in...will it still be possible for the phone to be bypassed and used....thats my first question,my second question is this...im aware iphone has find my network which allows the stolen phone even when switched off to use other apple devices to ping its location to find my but thats not working for me,is it because im in nigeria because most of the find my features i see online were really not available for me.

[Re-Titled by Moderator]