the tracking function also has a lock feature.
Step 1
Enable the "Find My iPhone" application on your phone while it is still in your possession. You cannot enable the application once the phone is lost or stolen. Go to the "Settings" application on your phone and choose "iCloud" from the menu. Toggle the icon next to "Find My iPhone" to the "On" position by tapping it once.
Step 2
Go to a computer as soon as possible after you realize your iPhone has been stolen. Point the Web browser to iCloud.com and log in using your Apple ID and password. Click on the "Find My iPhone" icon to initiate a search for your phone. Once your phone appears on the map, click on the "i" icon next to it. Click "Remote Lock" to stop anyone from using your phone.
http://smallbusiness.chron.com/make-sure-one-uses-iphone-stolen-33178.html
OR.....take your new, cheap replacement phone, go visit the alleged thief.
call your number.....