The exact same thing happened to my family, but we were a little smarter I suppose. We had poof the cell phone was stolen because we called the police as soon as it happened. Soon after, TMobile tried to slam us with a $5,600 phone bill because some dude made phone calls to Iran using our cell phone. Since it was stolen, my father (he's scary) threatened to sue TMobile and collect money because of causing anger, frustration, and temporary insanity (I'm not kidding lol), and they knuckled under, and said "Ok, Ok, we won't charge you."
That --- was awesome.
This happened about half a year ago and now we use Sprint. Hopefully the same issues will not occur if this unfortunate event happened again. We keep very close tabs on our things in my family, and now even closer with our cell phones. We created a special password to even use our cell phone, so no one can get it. My dad home brewed the program to create the password. Don't you just love computer science?