Firebase realtime database hiscore

Question

I want to get user's data (like nickname,country) who is champion. In my example I want to get data of nickname3 because who has 863 hiScore.It means nickname3 is champion.

I tried some thing but it is not working. In my opinion firstly I should find the champion's reference. After finding reference of champion, I can try get values of children of champion.

Can you help me. How can I get the values of the champion.

What I tried is

override fun getHiScoreInFirebase(interfaceCallback: InterfaceCallback) {

    var ref=FirebaseDatabase.getInstance().reference.child("user").orderByChild("HiScore").limitToLast(1).ref
    ref.addValueEventListener(object : ValueEventListener {
        override fun onDataChange(dataSnapshot: DataSnapshot) {
           if(dataSnapshot.exists()){

            val hiScore=   dataSnapshot.child("HiScore").getValue() as Int
            val kullaniciAdi=   dataSnapshot.child("KullaniciAdi").getValue() as String
            val sehir=  dataSnapshot.child("Sehir").getValue() as String
            val ulke= dataSnapshot.child("Ulke").getValue() as String

            interfaceCallback.hiScoreSonucCallback(hiScore,kullaniciAdi,ulke,sehir)

        }}

        override fun onCancelled(error: DatabaseError) {

        }


    })}