How to get my phone back?

[Sweg]

Last freaking year I got an Iphone 5 for Christmas. Two months later I was at practice and I hid it in my shoe, underneath my hoodie, inside my bag. And my bag was close to me. Well these girls (I knew one of them!) were waiting for their parents to pick them up while I was at practice, and they were sitting by my bag. Well I wasn't even looking at them because I was busy paying attention to my instructor. Well, it was break and the girls were gone, and my phone went missing! We called it, and the girl that I know picked up, and we asked them to please return the phone. They hung up. Well, I told our schools officer, and they did nothing about it. They said they will look at the security camera which WAS POINTING RIGHT AT MY BAG, but they never even looked at it.

Well, this school year came up and I saw her with my phone all the time. I got a crack on my phone by dropping it, and "her phone" has the exact same crack. AND she even admitted it to one of our mutual friends that she stole it! I told the principal in November, and he had one of our intervention specialists talk to her. All they did was ask her "Did you steal Julias phone?" And she simply said "No." And they believed her. They told me "I don't think she stole your phone. She said she didn't." Of course she's going to say fucking no! And right after that happened, she blocked me on every social media website (If that isn't sketchy enough).

Everyday I see that little bitch with my phone and I just want to so badly grab it from her and run, but I am kind of scared by her. She get's into a lot of fights and such, so I don't want to mess with her.

But how do I get it back! There's so much evidence that she has it! My school honestly has the worst way of dealing with things. Is there anyway or is it to late?
Oh and we have the serial number of the phone.
So I mean if my school actually cooperated with me, then they could have had our police officer go to the phones settings and see if the serial number matches. But hey, my school sucks!!

[Adan]

Bring your parents up to the school to talk to the principal. That should be make the other girl return your phone or have a conference with her parents. Otherwise, you could file a police report, but I'm not sure how far that would go.

[Inda Cloud]

You won't get it back. What you should have done was gone to your cell company, told them the phone was stolen, and then gone to the cops about it.

If you report a phone stolen, and it's done properly, no other service will turn it on - rendering the phone useless.

[Artemis Agrotera]

Last freaking year your parents should have made a police report.