How to block an iPhone with the serial number

my bag were i had my iphone 7 was stolen from me in Paris, i tried to plead with the robber by sending messages and email to my phone. i find out he is access my information through my iphone. now i have removed the iphone 7 from my Icloud and i don't want the phone to be useful to robber anymore so i was asked to block it. How do i block it with the serial number?

[Re-Titled by Moderator]