Lost iphone

If Find My iPhone is turned off, you no longer have access to the device. If you had a passcode on the device, the thief will have to restore it to remove the passcode, which will wipe all of the content, but with Find My iPhone off, they will be able to restore it and use it themselves. Report it to your carrier to disable the SIM, and see if they provide blacklisting services.

Either obtain the iPhone in your hand, tell the person holding it to reset it, or the reset cannot be done.

It’s too bad Find My iPhone is not set up.

If your iPhone, iPad, or iPod touch is lost or stolen - Apple Support

You can't factory reset an iPhone without direct access to a device.