My iPhone XS was stolen in NYC this last weekend!

Stolen iPhone while in NY this past weekend. I turned on Lost Mode in find iPhone app and applied contact info should someone turn in/on. I went thru AT&T insurance to receive replacement device. When we went to restore it wasn’t capturing latest backup so the rep told me to forget the old device. When I did that I received an email that now the Find my iPhone was disabled on previous phone and could be erase, reactivated and used by someone else. All I am concerned about is the information that was stored on my old iPhone. I had 6 digit code and face lock on this device. Is my info secure, at this point they can have the old phone but I don’t want my data being accessible by whoever may have now. Please help!